Battery Terms & Definitions



A metal alloy (e.g., LaNi5) capable of undergoing a reversible hydrogen absorption/desorption reaction as the battery is charged and discharged, respectively. This is the most popular electrode used in nickel metal hydride batteries. 

Absorbent Glass Mat (AGM):

A type of non-woven separator material composed almost entirely of glass microfibers that absorbs and retains the electrolyte, leaving no free electrolyte in the cell to spill. VRLA batteries made with this material are often referred to as "AGM" batteries. 


The taking up or retention of one material by another by chemical or molecular action.


A rechargeable battery or cell (see also Secondary battery).

Acid battery:

The battery in which acid is used as electrolyte, e.g.,lead-acid battery in which sulfuric acid is the electrolyte.

Acid Stratification:

When charging a traditional/flooded lead-acid cell, high-density acid is produced in the plates. This heavy acid drops as a result of gravitation to the lower part of the cell while lower density acid rises to the top of the cell. This stratification of acid can cause loss of capacity and/or battery failure. Acid stratification is a much smaller concern in AGM batteries. 


A type of chemical that can release hydrogen ions when mixed with water. Sulfuric acid is used in a lead-acid battery. 

Active Material:

Chemically active compounds in a cell or battery that convert from one composition to another while producing current (electrical energy) or accepting current from an external circuit. 

Actual Capacity or Available Capacity:

The total battery capacity, usually expressed in ampere-hours or milliampere-hours, available to perform work. The actual capacity of a particular battery is determined by a number of factors, including the cut-off voltage, discharge rate, temperature, method of charge and the age and life history of the battery.


See Absorbent Glass Mat


A primary battery (non-rechargeable) often used in electronics applications requiring heavy currents for long periods of time (i.e.: cd players, radios, etc.). Alkaline batteries can deliver 50-100% more total energy than conventional Carbon/Zinc batteries of the same size, hence their popularity in consumer applications.

Alkaline storage battery:

A battery which employs alkaline aqueous solution for its electrolyte. The Nickel-cadmium battery as designed.


A mixture of several other metals or a metal and a non-metal. 


A type of generator used in automobiles to produce electric current.

Ambient Humidity:

The average humidity of the surroundings. 

Ambient Temperature:

The average temperature of the battery's surrounding medium, typically air.

Ampere or Amp (A):

An Ampere or an Amp is a unit of measurement for an electrical current. One amp is the amount of current produced by an electromotive force of one volt acting through the resistance of one ohm. Named for the French physicist Andre Marie Ampere. The abbreviation for Amp is A but its mathematical symbol is "I". Small currents are measured in milli-Amps or thousandths of an Amp.

Ampere-Hour (Amp-Hrs, Ah):

A unit of measure for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge. (Example: A battery that delivers 5 amperes for 20 hours delivers 5 amperes x 20 hours = 100 amp-hrs of capacity.) 

Ampere-Hour Capacity:

The number of ampere-hours which can be delivered by a battery on a single discharge.


During discharge, the negative electrode of the cell is the anode. During charge, that reverses and the positive electrode of the cell is the anode. The anode gives up electrons to the load circuit and dissolves into the electrolyte.

Aqueous Batteries:

Batteries with water-based electrolytes. The electrolyte may not appear to be liquid since it can be absorbed by the battery’s separator.

Assembled Battery:

see Battery Pack



An electrochemical device used to store energy. The term is usually applied to a group of two or more electric cells connected together electrically. In common usage, the term “battery” is also applied to a single cell, such as a AA battery.

Battery Capacity:

The electric output of a cell or battery on a service test delivered before the cell reaches a specified final electrical condition and may be expressed in ampere-hours, watt- hours, or similar units. The capacity in watt-hours is equal to the capacity in ampere-hours multiplied by the battery voltage.

Battery Charger:

A device capable of supplying electrical energy to a battery to replensigh the batteries energy.

Battery Pack:

Two or more electrochemical cells electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term "battery" is often also applied to a single cell. 

Battery-Charge Rate:

The current expressed in amperes (A) or milli amps (mA) at which a battery is charged.

BCI Group:

The Battery Council International (BCI) Group Number "fingerprints" a battery with the following characteristics: (a) dimensions (L x W x H), (b) voltage (6V or 12V), (c) polarity (right-hand front positive, left-hand front positive, etc.), (d) type terminals (top, side, "L", etc.). The BCI Group Number does not designate a battery’s capacity; it merely defines the above-listed physical characteristics. 


A cylindrical cell design utilizing an internal cylindrical electrode and an external electrode arranged as a sleeve inside the cell container. 

Boost Charge:

The process of ensuring that the cells and plates within a battery are charged sufficiently for the battery to perform its desired function. Boost charging is typically done for a short duration at high current. 

Button Cell:

a battery cell with overall height less than its diameter. Button cells are manufactured with circular disc electrodes that are separated with a separator sheet


C-Rate (C) (also see Hourly Rate):

Discharge or charge current, in amperes, expressed in multiples of the rated capacity. For example, C/10 discharge current for a battery rated at 1.5 Ah is: 1.5 AH/I 0 = 150 mA (A cell's capacity is not the same at all discharge rates and usually increases with decreasing rate.) 


Chemical symbol: Cd. This metallic element is the chemically-active material of the Nickel-cadmium battery's negative electrode. When the battery is charged, the negative electrode surface consists of cadmium. As the battery discharges, the cadmium progressively changes into cadmium hydroxide (CdOH2).

Cadmium Hydroxide:

Active material used at the negative electrode of the Nickel-cadmium cell.

Cadmium Salt:

A chemical compound in which the hydrogen atom as been replaced by the cadmium atom: e.g.) 2HNO3 + Cd(OH)2 -> Cd(NO3)2 + 2H2O cadmium nitrate.


The capacity of a battery is a measure of the amount of energy that it can deliver in a single discharge. Battery capacity is normally listed as amp-hours (or milli amp-hours) or as watt-hours.

Capacity Offset:

A correction factor applied to the rating of a battery if discharged under different C-rates from the one rated. 

Capacity Retention (or Charge Retention):

The fraction of the fall capacity available from a battery under specified conditions of discharge after it has been stored for a period of time 


A primary battery (non-rechargeable) commonly used in low drain consumer applications (i.e.: clocks, calculators, garage door openers, etc.). Available in the same sizes as the Alkaline and Manganese Dioxide ("AA", "AAA", 9volt, "C", "D") the Carbon/Zinc is one of the most widely used dry primary batteries because of its low cost and reliable performance. 


Is an electrode that, in effect, oxidizes the anode or absorbs the electrons. During discharge, the positive electrode of a voltaic cell is the cathode. When charging, that reverses and the negative electrode of the cell is the cathode.

CCA: (Cold Cranking Amps):

is a rating used in the battery industry to define a battery’s ability to start an engine in cold temperatures. A great amount of amperes is needed to start the engine, but only for a short time.The actual rating is the number of amps that can be removed from a new fully charged battery at 0°F for 30 seconds while maintaining a voltage of at least 7.2 volts (for a 12-volt battery).As a battery ages with use, it may no longer be able to meet its original CCA rating.The higher the CCA rating, the greater the starting power of the battery. 


An electrochemical device, composed of positive and negative plates and electrolyte, which is capable of storing electrical energy. It is the basic “building block” of a battery.

Cell Mismatch:

Cells within a battery pack that contain different capacity and voltage levels. 

Cell Reversal:

The stronger cells of a battery (several cells connected in series) impose a voltage of reverse polarity across a weaker cell during a deep discharge. 

Change in Temperature (ΔT):

charge termination based on difference between ambient temperature and cell temperature

Change in Temperature/Change in Time (dT/dt):

charge termination based on change in temperature over time. This termination is meant to detect rapid temperature increases created just before a battery or cell reaches its full charge. Normal dT/dt is 1°C/minute


The conversion of electric energy, provided in the form of a current, into chemical energy within the cell or battery.

Charge Acceptance:

The quantity of current in ampere-hours which a battery in a defined charge state can accept at a specified temperature and charge voltage within a defined period. 

Charge Control:

Technique for effectively terminating the charging of a rechargeable battery. 

Charge Efficiency:

ratio of a cell's output during discharge to its input during charge. Ratio can be expressed in efficiency of capacity, nominal voltage, or power

Charge Rate:

current applied to a cell to restore its capacity. Charge rate is usually expressed in terms of the cell's C Rate. This rate is also commonly expressed as a fraction of the capacity of the battery. For example, the C/2 or C/5.

Charge Retention:

Residual capacity after a period of storage of a fully charged battery.

Charge, State of:

The capacity remaining in a cell or battery.

Chemical cells:

The type of cells which convert energy obtained by chemical reactions into electrical current. Most of the popularly used cells belong to this group.


An electrical circuit is the path followed by a flow of electrons. A closed circuit is a complete path. An open circuit has a broken, or disconnected, path. 

Circuit (Parallel):

A circuit that provides more than one path for the flow of current. A parallel arrangement of batteries (usually of like voltages and capacities) has all positive terminals connected to a conductor and all negative terminals connected to another conductor. If two 12-volt batteries of 50 ampere-hour capacity each are connected in parallel, the circuit voltage is 12 volts, and the ampere-hour capacity of the combination is 100 ampere-hours. 

Circuit (Series):

A circuit that has only one path for the flow of current. Batteries arranged in series are connected with negative of the first to positive of the second, negative of the second to positive of the third, etc. If two 12-volt batteries of 50 ampere-hours capacity each are connected in series, the circuit voltage is equal to the sum of the two battery voltages, or 24 volts, and the ampere-hour capacity of the combination is 50 ampere-hours. 

Closed-circuit Voltage(CCV):

The potential or voltage of a battery when it is discharging or charging. 

Cold-cranking Amps (CCA):

Number of amperes a lead-acid battery at 0oF (-17.8oC) can deliver for 30 seconds and maintain at least 1.2 volts per cell. 


A process that utilizes a series of heavy discharges and recharges on a battery to assure optimum performance. 


The ability to transmit current in a circuit or battery. 

Constant current charge:

A charge during which the current is maintained at a constant value. Sealed nickel-cadmium batteries are normally charged at a constant.

Constant Current:

A battery discharge regime whereby the current drawn during the discharge Discharge remains constant. 

Constant Power:

A battery discharge regime whereby the current during the discharge increases as the battery voltage decreases. 

Constant Resistance:

A battery discharge regime whereby the resistance of the equipment load remains constant throughout discharge. 

Constant voltage charge:

A charge during which the voltage across the battery terminals is maintained at a constant value. This method is not normally used for sealed nickel-cadmium cells or batteries.

Constant-Current Charge:

A charging process in which the current applied to the battery is maintained at a constant value.


The polypropylene or hard rubber case which holds the plates, straps and electrolyte. 

Continuous Test:

A test in which a battery is discharged to a prescribed end point voltage without interruption. 


The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces deterioration of the material and its properties. The positive lead grids in a battery gradually corrode in service, often leading to a battery failure. Battery terminals are subject to corrosion if they are not properly maintained. 


A unit to measure the in-going charge and out-going discharge current of a battery. A coulomb is equal to the electricity transferred by a current of one ampere in one second. (The maximum energy a molecular weight of a chemical system can deliver is one Faraday of energy or 96,500 coulombs which is the equivalent of 26.8Ah of capacity.


The lid for the container. 

Current (Alternating) (AC):

A current that varies periodically in magnitude and direction. A battery does not deliver alternating current. 

Current (Direct) (DC):

An electrical current flowing in an electrical circuit in one direction only. A secondary battery delivers direct current and must be recharged with direct current in the opposite direction of the discharge. One terminal is always positive and another is always negative.


The rate of flow of electricity, or the movement of electrons along a conductor. It is comparable to the flow of a stream of water. The unit of measure for current is the ampere. 

Current Collector:

An inert structure of high electrical conductivity used to conduct current from or to an electrode during discharge or charge. 

Current Density:

The current per unit active area of the surface of an electrode. 

Current Drain:

The current withdrawn from a battery during discharge. 

Current Limiting Chargers:

A charger that keeps the charge current constant during the charge process but allows the voltage to Fluctuate (typically used on NiCd and NiMh chargers). 

Cutoff Voltage:

The battery voltage at which the discharge is terminated. The cutoff voltage is specified by the battery manufacturer and is generally a function of discharge rate. 

Cutoff Voltage, final:

The prescribed lower-limit voltage at which battery discharge is considered complete. The cutoff or final voltage is usually chosen so that the maximum useful capacity of the battery is realized. The cutoff voltage varies with the type of battery and the kind of service in which the battery is used. When testing the capacity of a NiMH or NiCD battery a cutoff voltage of 1.0 V is normally used. 0.9V is normally used as the cutoff voltage of an alkaline cell. A device that is designed with too high a cutoff voltage may stop operating while the battery still has significant capacity remaining.

Cycle Life:

For rechargeable batteries, the total number of charge/discharge cycles the cell can sustain before it’s capacity is significantly reduced. End of life is usually considered to be reached when the cell or battery delivers only 80% of rated ampere- hour capacity. NiMH batteries typically have a cycle life of 500 cycles, NiCd batteries can have a cycle life of over 1,000 cycles. The cycle of a battery is greatly influenced by the type depth of the cycle (deep or shallow) and the method of recharging. Improper charge cycle cutoff can greatly reduce the cycle life of a battery.

Cycle use:

A method of battery use involving repeated charging and discharging.


A sequence where a charged battery is discharged and recharged. 

Cylindrical Cell:

The positive and negative plates are rolled up and placed into a cylindrical container (as opposed to stacking the plates in a prismatic cell design). 


Deep Cycle:

A cycle in which the discharge is continued until the battery reaches it’s cut-off voltage, usually 80% of discharge.

Deep Cycling:

Application in which the cell or battery is successively and repeatedly charged, then completely and fully discharged.

Deep Discharge:

Discharge of at least 80% of the rated capacity of a cell or battery.

Deep-Cycle Battery:

Battery that provides a steady amount of current over a long period of time. It provides a surge when needed and is designed to be deeply discharged over and over again. 

Delta V:

Detecting the voltage drop which indicates a cell is fully charged. See "negative Delta V (-ΔV)"


see "memory effect"

Depth of Discharge (DOD):

The amount of energy that has been removed from a battery (or battery pack). Usually expressed as a percentage of the total capacity of the battery. For example, 50% depth of discharge means that half of the energy in the battery has been used. 80% DOD means that eighty percent of the energy has been discharged, so the battery now holds only 20% of its full charge.


The opposite of absorption, whereby the material retained by a medium or another material is released. 

Direct Current (DC):

See Current (Direct) (DC)


The conversion of the chemical energy of the battery into electric energy.

Discharge capacity:

Capacity that can be discharged from a battery. The unit as Ah, (ampere-hour).

Discharge Rate:

rate at which electrical current is removed from a cell or battery, usually measured in milli-amperes (mA) or multiples of the C Rate

Discharge Voltage:

voltage a battery's or cell's terminals during discharge

Discharge, high-rate:

Withdrawal of large currents for short intervals of time, usually at a rate that would completely discharge a cell or battery in less than one hour.

Discharge, low-rate:

Withdrawal of small currents for long periods of time, usually longer than one hour.


The current withdrawn from a battery during discharge. 

Dry Cell:

A primary cell in which the electrolyte is absorbed in a porous medium, or is otherwise restrained from flowing. Common practice limits the term “dry cell” to the Leclanch‚ cell, which is the common commercial type.

Dumb Battery:

Straight battery pack without internal circuits enabling communication between the battery and the user. 

Duty Cycle:

The operating regime of a battery including factors such as charge and discharge rates, depth of discharge, cycle duration, and length of time in the standby mode. 



Discharge or charge power, in watts, expressed as a multiple of the rated capacity of a cell or battery that is expressed in watt-hours. For example, the E/10 rate for a cell or battery rated at 17.3 watt-hours is 1.73 watts. (This is similar to the method for calculating C-Rate.) 

Electric Current:

The movement of electrons along a conductor. 

Electrochemical Couple:

The system of active materials within a cell that provides electrical energy storage through an electrochemical reaction.

Electrochemical Equivalent:

Weight of a substance that is deposited at an electrode when the quantity of electricity which is passed is one coulomb 


An electrical conductor through which an electric current enters or leaves a conducting medium, whether it be an electrolytic solution, solid, molten mass, gas, or vacuum. For electrolytic solutions, many solids, and molten masses, an electrode is an electrical conductor at the surface of which a change occurs from conduction by electrons to conduction by ions. For gases and vacuum, the electrodes merely serve to conduct electricity to and from the medium.


A chemical compound which, when fused or dissolved in certain solvents, usually water, will conduct an electric current. All electrolytes in the fused state or in solution give rise to ions which conduct the electric current.

Electrolyte Retention Capability:

The degree to which a separator retains electrolyte.


Negatively charged particle that orbits the nucleus of an atom. 

Electronic Tester:

An electronic device that assesses the condition of a battery through an ohmic measurement such as resistance or conductance, typically without drawing large current loads. 


The degree to which an element in a galvanic cell will function as the positive element of the cell. An element with a large electropositivity will oxidize faster than an element with a smaller electropositivity.


A set of positive and negative plates assembled with separators. 

End Voltage Cutoff:

The prescribed voltage at which the discharge (or charge, if end-of-charge voltage) of a battery may be considered complete. 

End voltage:

The voltage that indicates the end limit of discharge. This voltage is almost equivalent to capacity in practical use.

End-of-Discharge Voltage:

The voltage of the battery at termination of a discharge.


heat absorption caused by a chemical reaction

Energy - Output Capability:

expressed as capacity times voltage, or watt-hours.

Energy Density:

Ratio of cell energy to weight or volume (watt-hours per pound (Wh/L), or watt-hours per cubic inch(Wh/kg)).


overall amount of power a battery or cell can deliver over time. Product of the battery's or cell's voltage, discharge rate, and discharge time. Usually expressed in milli-Watt hours (mWhr) or mWhr = V x mA x hrs

Equalization Charge:

The process of ensuring that the cells and plates within a battery are all at full charge and that the electrolyte is uniform and free of stratification. This is normally done by charging the battery under controlled conditions (charge current, time and upper voltage limits are usually specified). 


Commonly understood as one or more discharge cycles to one volt per cell with subsequent recharge. Used to maintain NiCd & NiMH batteries.


release of heat caused by a chemical reaction


Fast Charge:

Rate of charging a cell or battery to full charge capacity in 2 1/2 hours or less

Final Voltage (see Cutoff voltage)

Float Charging:

Method of recharging in which a secondary cell is continuously connected to a constant-voltage supply that maintains the cell in fully charged condition. Typically applied to lead acid batteries.


The use of batteries in which they are charged by an application to be ready for use if the primary power to the application fails. Also called standby or backup. 


Positive electrode made with a porous nickel metal instead of a nickel sintered strip. Thicker and porous, it holds more active material greatly increasing it's capacity.

Forced Discharge:

Discharging a cell in a battery, by the other cells or an external power source, below zero volts into voltage reversal. 


In battery manufacturing, formation is the process of charging the battery for the first time. Electrochemically, formation changes the lead oxide paste on the positive grids into lead dioxide and the lead oxide paste on the negative grids into metallic sponge lead. 


Device used for cutting off an electrical current in the event of an abusive condition. 


Galvanic Cell:

A combination of electrodes, separated by electrolyte, that is capable of producing electrical energy by electrochemical action.

Gas permeability:

The degree of mobility of gas through porous film, fabric or other plate-separating material.

Gas recombination on negative electrode:

The method to suppress hydrogen generation by recombining oxygen gas on the negative electrode, and making the negative electrode chemically discharged when oxygen gas is generated at the positive electrode at the end of charging.


The evolution of gas from one or more of the electrodes in a cell. Gassing commonly results from local action (self-discharge) or from the electrolysis of water in the electrolyte during charging. 


Electrolyte that has been immobilized by the addition of a chemical agent, normally fine silica, to prevent spillage. Batteries made with gelled electrolyte are often referred to as gel batteries. Gel batteries are one typical type of VRLA battery. 


A device that produces an electric current through magnetism. 

Gravimetric Energy Density:

ratio of a battery's or cell's energy to its weight. Also called power density. Usually expressed in Watt-Hours per kilogram (Wh/kg)


Lead alloy framework that supports the active material of a battery plate and conducts current. 


Reference potential of a circuit. In automobile use, the result of attaching the battery cable to the body frame which is used as a path for completing a circuit in lieu of a direct wire from a component. Today, over 99 percent of autos use the negative terminal of the battery as the ground. 

Group Size:

The Battery Council International (BCI) assigns numbers and letters for common battery types. There are standards for maximum container size, location and type of terminal and special container features. 


Hazardous Waste:

Waste which is classified as "hazardous" (i.e.. potentially harmful to the environment) by the government. 

Hertz (Hz):

The standard unit of frequency. A frequency of one complete cycle per second is a frequency of one hertz. 

High rate discharge:

Discharge at a comparatively high current rate in comparison with cell capacity.

Hour rate:

The hour rate is associated with both discharging and charging the battery, and is expressed in terms of discharge time at its nominal capacity rating. "H-hou" represents the length of time it takes to discharge a battery, and "i" represents the rate of discharge.


A device used to measure the strength (i.e., the concentration of sulfuric acid in the electrolyte) of the electrolyte through specific gravity of the electrolyte. 



International Electrotechnical Commission, a non-profit, non-governmental international standards organization. Prepares and publishes international standards for all electrical, electronic, and related technologies

Impedance Intermittent Test:

Used in terms of the battery's internal resistance a test during which a battery is subjected to alternate periods of discharge and rest according to a specified discharge regime. 


Used in terms of the battery's internal resistance.

Intelligent battery:

Battery with internal circuit enabling some communication between the battery and user. Some batteries feature a capacity indicator only, others offer an external bus to interface with the equipment the battery powers and the intelligent charger.


reaction where lithium ions are reversibly removed or inserted into a hose without a significant structural change taking place

Intercell Connectors:

Lead structures that connect adjoining cells in series, positive of one cell to the negative of the next, within a battery. 

Internal Impedance:

The opposition exhibited by a circuit element (cell or battery) to the flow of an alternating current (a/c.) of a particular frequency as a result of resistance, induction and capacitance. 

Internal Pressure:

pressure within a sealed battery or cell caused by oxygen or hydrogen evolution

Internal Resistance (IR):

The opposition exhibited by a circuit element to the flow of direct current (D.C.). In a cell, the internal resistance is the sum of the ionic and electronic resistances of the cell components. 


a space between closely set things, or between the parts which compose a body. A narrow chink; a crack, crevice, or hole


An atom or a group of atoms charged either positively or negatively.

IR Drop:

A voltage drop associated with the electrical resistance (R) of a battery or current flow (I). The voltage drop is the product of the current (in amperes) and the resistance (in ohms). 




Lead Acid:

Still the most popular battery used today its main application is for the automobile industry, although it has a growing number of other applications. Its advantages are low cost, high voltage per cell and good capacity life. Disadvantages are poor low temperature characteristics, it is relatively heavy, and it cannot be left in a discharged state for too long without being damaged. Related Batteries: Absorbent Glass Matt (AGM) Gel/Gel Cell Sealed Lead Acid 

Lead-Acid Battery:

Battery made up of plates, lead and lead oxide (various other elements are used to change density, hardness, porosity, etc.) with a 35 percent sulfuric acid and 65 percent water solution. This solution is called an electrolyte, which causes a chemical reaction that produce electrons. 


The escape of electrolyte to the outer surface of the battery.

Limiting Current:

The maximum current drain under which the particular battery will perform adequately under a continuous drain. The rate is based on whatever drain rate reduces the running voltage to 1.1 volts. 

Lithium Cobaltite (LiCoO2):

dark blue, water-insoluble powder. Exhibits both the fluxing properties of lithium oxide and the adherence-promoting properties of cobalt oxide. Intercalates lithium ions in battery and cell applications.

Lithium Ion (Li Ion):

One of the newer rechargeable battery technologies, Li Ion batteries can deliver 40% more capacity than comparably sized NiCd batteries and are one of the lightest rechargeable batteries available today. Li Ion batteries are the batteries of choice in notebook computer, wireless telephones and many camcorder models. They are also one of the more expensive rechargeable technologies. 

Lithium Ion:

advanced chemistry/technology for primary and secondary batteries. Offers increased performance and twice the energy density of nickel-based batteries. There are several major varieties of lithium ion battery technology, each of which has unique properties. Lithium ion secondary batteries can charge to full capacity in as little as 3 hours

Lithium Iron Phosphate:

a variety of lithium ion chemistry/technology that offers high discharge rate capability, long cycle life, and long calendar life

Lithium Polymer:

a variation of lithium ion battery which differs only construction—chemistry is the same. Lithium polymer allows for very flexible packaging, lower cost, and safer operation

Lithium Primary Battery:

have the highest specific energy (energy by weight) and energy density (energy by volume) of all primary battery types. Have open circuit voltages (OCVs) between 2.7 and 3.6V. Their relatively high internal impedance limits them mostly to low drain applications


A primary battery (non-rechargeable) that is quickly entering mainstream electronic designs, particularly in consumer, portable equipment and non-volatile memory back up applications where small size, long life and low cost are the primary requirements. Lithium batteries have superior cold temperature performance and a shelf life of 5-10 years. 

Load Current:

The discharge current provided by a battery, or drawn by a battery powered device. 

Load Tester:

An instrument that draws current (discharges) from a battery using an electrical load while measuring voltage. It determines the battery’s ability to perform under actual discharge conditions. 

Low Water-Loss Battery:

A battery that does not require periodic water addition under normal driving conditions; also referred to as a maintenance-free battery. 

Low-Voltage Disconnect (Cutoff):

voltage-sensing device to automatically disconnect a battery or cell from a load at predetermined voltage. Low-voltage disconnects prevent cell reversal during discharge.


Maintenance Charge (Float Charge):

method for maintaining the charge of a battery or cell by continuously charging it at a rate sufficient to balance its self-discharge

Maintenance-Free Battery:

Battery in which you don't have to check or refill the electrolyte levels. 

Manganese Dioxide Lithium:

generally equivalent to poly batteries and cells in construction, energy density, safety and OCV, though with roughly half the service life. Well-suited to applications with high continuous- or pulse-current requirements due to their lower internal impedance. Available in standard cylindrical and coin styles

Manganese Dioxide:

A primary battery (non-rechargeable) similar to that of the alkaline battery though not as strong in total energy. Available in the same size as Alkaline and Carbon/Zinc ("AA", "AAA", "C","D", 9volt) the Manganese Dioxide chemistry is noted for its ability to retain its charge while being stored at high temperatures and operates well at temperatures as low as -40C with little loss of capacity. 

Matched cells:

Cells carefully selected by the factory to display within 5% of the same capacity at the time of manufacturer.

MCA (Marine):

MCA is an industry rating defining a marine battery’s ability to deliver a large amount of amperage for a short period of time. Since marine batteries are typically never used at temperatures below freezing, marine cranking amps are measured at 32°F as opposed to 0°F for cold cranking amps. The rating is the number of amps that can be removed from a marine battery at 32°F for 30 seconds while maintaining a voltage of at least 7.2 volts for a 12-volt battery. The higher the MCA rating, the greater the starting power of the marine battery. 

Memory Effect (Voltage Depression):

A phenomenon in which a cell, operated in successive cycles to less than full, depth of discharge, temporarily loses the remainder of its capacity at normal voltage levels (usually applies only to Ni-Cd cells). Note, memory effect can be induced in NiCd cells even if the level of discharge is not the same during each cycle. Memory effect is reversable.

Metal Hydride:

An intermetallic compound or alloy in which hydrogen has been absorbed-, also, the negative electrode in a nickel-metal hydride battery. 

Midpoint Voltage:

The voltage of a battery midway in the discharge between the start of the discharge and the end voltage. 


movement of charged ions under the influence of a potential gradient


Refers to battery capacity. A 1/1000th of an amp, e.g.: 1.0Ah = 1000mAh. 

Misch Metal (M):

matrix of the negative electrode of a battery or cell. Composed of hydrogen-storing alloys

Mobility of ions:

Velocity of ions moving in electrolyte between electrodes of opposite polarity.


Negative Delta V (-ΔV):

charge termination based on detecting a decrease in voltage which indicates a cell or battery is charged. Designed to terminate charge as over-charge starts

Negative Electrode:

electrode in a battery or cell acting as the anode during discharge. Composed of hydrogen-storing alloys. Also called the minus electrode.

Negative Terminal:

The terminal of a battery from which electrons flow in the external circuit when the cell discharges. See Positive Terminal.

Nickel Cadmium:

One of the most proven and historically most widely used rechargeable batteries. Very dependable and "robust" but contain cadmium and have relatively low capacity when compared to other rechargeable systems. Very good high rate discharge capabilities make them very popular in high drain applications such as power tools. 

Nickel hydroxide:

Active material used at the positive electrode of the Nickel-cadmium cell.

Nickel Metal Hydride (NiMh):

Interchangeable with most NiCd batteries, nickel metal hydride (NiMh) batteries generally deliver 10-25% greater capacity than NiCds and are environmentally more friendly than NiCds since they do not contain cadmium. Used in many wireless phone and camcorders. 

Nickel Tab:

mechanical connector used to electrically connect cells in a battery pack

Nominal capacity:

The standard capacity designated by a battery manufacturer to indentify a particular cell model.

Nominal Voltage:

The characteristic operating voltage or rated voltage of a battery. 

Nonaqueous Batteries:

Cells that do not contain water, such as those with molten salts or organic electrolytes.



A measure of resistance that causes one volt to produce a current of one ampere. 

Ohm’s Law:

The formula that describes the amount of current flowing through a circuit. Ohm's Law - In a given electrical circuit, the amount of current in amperes (I) is equal to the pressure in volts (V) divided by the resistance, in ohms (R). Ohm's law can be shown by three different formulas:

Open Circuit:

Condition of a battery which is neither on charge nor on discharge (i.e., disconnected from a circuit).

Open-Circuit Voltage (OCV):

The difference in potential between the terminals of a cell when the circuit is open (i.e., a no-load condition). The voltage of a battery when it is not delivering or receiving power. 

Operating voltage:

Voltage between the two terminals of the battery without any load.


The forcing of current through a cell after all the active material has been converted to the charged state, that is, continued charging after reaching 100 percent state-of-charge. 


The process of discharging a cell or battery beyond its cutoff voltage and possibly into voltage reversal. 


the difference between the actual potential of electro-chemical reaction and the theoretical value at which the reaction becomes balanced.


A chemical reaction that results in the release of electrons by an electrode’s active material.

Oxygen Recombination:

process in which oxygen generated at the positive electrode of a battery or cell during over-charge reacts with hydrogen at its negative electrode, producing water


Parallel Connection:

The arrangement of cells in a battery made by connecting all positive terminals together and all negative terminals together. The voltage of the group remains the same as the voltage of the individual cell. The capacity is increased in proportion to the number of cells.


The phenomenon by which a metal, although in conditions of thermodynamic instability, remains indefinitely unattacked because of modified or altered surface conditions. 


Plastic Bonded Electrodes. PBE utilizes a manufacturing technique that produces a high-energy density negative electrode that allows higher capacity for a given cell size and a greatly reduced self discharge.

Peak Voltage Detection (PVD):

automatic charge termination based on the battery or cell being charged reaching peak voltage. Designed to terminate charge just as over-charge begins

Permanent charge:

The charging current which can be continuously maintained, regardless of the state of charge of the cell.

Plate - Negative:

Cast metallic frame that contains a spongy lead active material. 

Plate - Positive:

Cast metallic frame that contains the lead dioxide active material. 


Thin, flat structures composed of a grid and active material. The grid supports the active material and conducts electrons out of the cell. Plates are either positive or negative, depending on the active material they hold. 


Refers to the charges residing at the terminals of a battery.

Polarity reversal:

Reversing of polarity of the terminals of a small-capacity cell in a multi-cell battery due to overdischarge.


The lowering of the potential of a cell or electrode from its equilibrium value caused by the passage of an electric current. 


The term expressing the porous degree of a sintered plate. The equation for its calculation is: Porosity = (V1/V2) x 100. V1 is the volume of pores and V2 is the total volume of the plate including pores.

Positive Electrode:

electrode of a battery or cell acting as the cathode during discharge. Composed of nickel base (Ni) or nickel hydroxide

Positive Temperature Coefficient Device (PTC) or Thermostat:

safety device used in battery packs. At a predetermined temperature threshold, internal resistance goes from a low-resistance state to a high-resistance one to provide over-current and over-temperature protection

Positive Terminal:

The terminal of a battery toward which electrons flow through the external circuit when the cell discharges. See Negative Terminal.


Designating, or pertaining to, a kind of electrical potential; opposite of negative. A point or terminal on a battery having higher relative electrical potential. The positive battery terminal is the point to which electrons flow during discharge. 

Potassium Hydroxide (KOH):

electrolyte providing ion transport mechanism between the electrodes of NiMH cells

Potential of oxygen evolution:

Oxygen gas evolves due to the electrolysis of water in the battery being charged when it reaches a certain potential. This is called the potential of oxygen evolution.


energy of an electrical charge, measured by its power to perform work; electro-motive force. Potential energy per unit charge is voltage.


time rate of energy transfer, measured in Watts (W). Product the voltage (V) across a battery or cell and the current (A) through the battery or cell. W = V x A

Primary Battery:

A battery which is not intended to be recharged and is discarded when the battery has delivered all of its electrical energy. 

Primary Cell:

A cell designed to produce electric current through an electrochemical reaction that is not efficiently reversible. The cell, when discharged, cannot be efficiently recharged by an electric current. Alakline, lithium, and zinc air are common types of primary cells.

Prismatic Cell:

The positive and negative plates are stacked rather than rolled as done in a cylindrical cell. 

Pulse Current:

A periodic current drain of higher than normal drain rates. 

Pulse discharge:

A high-rate discharge, usually of 1 second or less.


Quantity of charge:

The amount of electric energy supplied to a battery. Its unit is Ah, (ampere-hour.)

Quick charge:

A method of charge an Nickel-cadmium battery for a short time at a high current level.


Rapid Charge:

rate of charging a battery or cell to full charge capacity in 2 1/2 to 6 hours

Rated Capability:

maximum charge/discharge rate of a battery or cell. Expressed in a multiple of the C rate

Rated Capacity:

The number of ampere-hours a cell can deliver under specific conditions (rate of discharge, end voltage, temperature); usually the manufacturer’s rating.


Capable of being recharged; refers to secondary cells or batteries.

Rechargeable Battery or Cell:

see "secondary batteries"


The action by which oxygen gas produced on overcharge is recombined chemically to avoid venting of a sealed cell and loss of water from the electrolyte. See "oxygen recombination"


One or more deep discharge cycles below 1.0 volt/cell at a very low, controlled current. Recondition helps to revert large crystals to small desirable sized, often restoring the battery to it's full capacity. 


Reclamation of materials without endangering human health and the environment. Nickel-cadmium cells are fully recyclable.


A chemical process that results in the acceptance of electrons by an electrode’s active material.

Resealable Safety Vent:

resealable vent built into cylindrical and prismatic cells which prevents the build up of high internal pressures

Reserve Capacity Rating (RC):

Number of minutes a battery at 26.7o C/80o F can be discharged at a 25-amp rate until reaching 10.5 volts (for a 12 volt battery) and maintaining 10.5 volts for a 12 volt battery. The higher the rating, the longer your vehicle can operate should your alternator or fan belt malfunction. 

Residual capacity:

The capacity remaining in a battery after field use, prior to charge.


The degree to which the flow of electrons is opposed by the material the electrons must pass through. Resistance is expressed in OHMS. 

Reversal charge:

The Nickel-cadmium cell is reverse-charged when connected to a charger in the wrong way, and current is forced to flow from the negative to positive electrodes, contrary to the direction of flow during normal charge. Here polarity is reversed, but all electric energy is consumed to generate gas.

Reverse load charge:

Charge method that intersperses discharge pulses between charge pulses to promote the recombination of gases generated during fast charge. Reverse Load charge also helps to reduce memory.


Safety vent:

A safety mechanism that is activated when the internal gas pressure rises above a normal level. There are two types: Automatically resealable, and unresealable.


The structural part of a galvanic cell that restricts the escape of solvent or electrolyte from the cell and limits the ingress of air into the cell (the air may dry out the electrolyte or interfere with the chemical reactions).

Sealed Battery:

Battery in which you don't have to check or refill the electrolyte levels. Leak-proof at angles over 45 degrees, also called VRLA (Valve Regulated Lead-Acid). 

Sealed cells:

A cell which remains closed and does not release either gas or liquid when operated within the limits of charge and temperature specified by the manufacturer. The cell cannot receive addition to the electrolyte.

Secondary Batteries (Rechargeable):

a battery or cell in which passing electrical current through it in the opposite direction of its discharge can reverse the electrochemical process, recharging the battery or cell. Commonly called rechargeable batteries.

Secure Waste Landfill:

A landfill designed for disposal of normal household trash but which meets government standards designed to protect the environment. 

Self Discharge:

Discharge that takes place while the battery is in an open-circuit condition.


The permeable membrane that allows the passage of ions, but prevents electrical contact between the anode and the cathode. Separators are made from numerous materials such as polyethylene, polyvinyl chloride, rubber, glass fiber and cellulose. 

Series Connection:

The arrangement of cells in a battery configured by connecting the positive terminal of each successive cell to the negative terminal of the next adjacent cell so that their voltages are cumulative. See Parallel Connection.

Service Life:

The period of useful life of a battery before a predetermined end-point voltage is reached. 

Shallow Cycling:

Charge and discharge cycles which do not allow the battery to approach it’s cutoff voltage. Shallow cycling of NiCd cells lead to “memory effect”. Shallow cycling is not detrimental to NiMH cells and it is the most beneficial for lead acid batteries.

Shelf Life:

The duration of storage under specified conditions at the end of which the battery still retains the ability to give a specified performance. 

Short Circuit:

An unintended current-bypass in an electric device or wiring, generally very low in resistance and thus causing a large amount of current to flow. In a battery, a cell short circuit may be damaging enough to discharge the cell and render the battery useless. 

Short-Circuit Current:

That current delivered when a cell is short-circuited (i.e., the positive and negative terminals are directly connected with a low-resistance conductor).


A primary battery (non-rechargeable) it is a major contribution to miniature power sources, and is well suited for hearing aids, instruments, photoelectric exposure devices and electronic watches. These cells are primarily made in the smaller button sizes.

Sintered electrode:

Sintered electrodes were originally developed by Saft and utilized nickel powder to form a highly porous metal sponge. The pores of this material are impregnated with the active material, yielding high discharge performance and very long life.

Sintered plaque:

A thin nickel-plated grid on which nickel powder has been coated.

SLA (Sealed Lead Acid):

An inexpensive secondary battery using lead

Slow charge:

Typically an over-night charge lasting about 14 hours at a charge current of 0.1C. Battery does not require instant removal when fully charged.

Smart Battery:

Battery with internal circuit enabling some communication between the battery and the user. Some batteries feature a capacity indicator only, others offer an external bus to interface with the equipment the battery power and the intelligent charger. 

Soft Cell:

A cell whose voltage rises above its defined boundaries during charging. This voltage rise may be caused by high cell impedance as a result of prolonged battery storage, very cold battery temperature or lack of electrolyte. 

Specific Energy:

The ratio of the energy output of a cell or battery to its weight (Wh/kg). This term is used interchangeably with gravimetric energy density. 

Specific Gravity (Sp. Gr. or SG):

Specific gravity is a measure of the electrolyte concentration in a battery. This measurement is based on the density of the electrolyte compared to the density of water and is typically determined by the use of a hydrometer (see Hydrometer). By definition, the specific gravity of water is 1.00 and the specific gravity of the sulfuric acid electrolyte in a typical fully charged battery is 1.265-1.285. Specific gravity measurements are typically used to determine if the battery is fully charged or if the battery has a bad cell. 

Spiral Wound:

An electrode structure of high surface area created by winding the electrodes and separator into a spiral-wound jelly-roll configuration. 

Splash Barrel:

A splash barrel is part of the battery's vent system. Its purpose is to keep acid out of the vents when the battery is upright as acid is splashed around in the cell from motion and vibration. 

Stand-by use:

The use of cells or batteries in which they are constantly charged so as to be always ready for use.

Standard Charge:

C/10 charge at 25°C for 16 hours. Sometimes called an overnight charge.


The use of batteries in which they are charged by an application to be ready for use if the primary power to the application fails. Also called float or backup. 

Starting, Lighting, Ignition (SLI) Battery:

Rechargeable battery that supplies electric energy to an automobile to power the starter motor, the lights and the ignition system of a vehicle’s engine. 

State of Charge (or State of Health):

The amount of deliverable low-rate electrical energy stored in a battery at a given time expressed as a percentage of the energy when fully charged and measured under the same discharge conditions. If the battery is fully charged, the state of charge is said to be 100 percent. 

Stationary Battery:

A secondary battery designed for use in a fixed location.

Storage Battery:

An assembly of identical cells in which the electrochemical action is reversible so that the battery may be recharged by passing a current through the cells in the opposite direction to that of discharge. While many non-storage batteries have a reversible process, only those that are economically rechargeable are classified as storage batteries. Synonym: Accumulator; Secondary Battery. See Secondary Cell.

Storage Cell:

An electrolytic cell for the generation of electric energy in which the cell after being discharged may be restored to a charged condition by an electric current flowing in a direction opposite the flow of current when the cell discharges. Synonym: Secondary Cell. See Storage Battery.

Storage Life:

see "shelf life"


The unequal concentration of electrolyte due to density gradients from the bottom to the top of a cell. This condition is encountered most often in batteries recharged from a deep discharge at constant voltage without a great deal of gassing. Continued deep cycling of a stratified battery will soften the bottoms of the positive plates. Equalization charging is a way to avoid acid stratification. 


Growth of lead sulfate crystals in Lead-Acid batteries which inhibits current flow. Sulfation is caused by storage at low state of charge. 

Sulfur Dioxide Lithium:

used almost exclusively in military/aerospace applications. These cells have somewhat lower energy density than manganese dioxide lithium or poly lithium cells. Service life and energy density are generally less than half that of thionyl chloride lithium cells. Require emergency vent structures for safety reasons



The mechanical lug used to connect cells together to form a battery or to connect it to equipment.

Taper Charge:

A charge regime delivering moderately high-rate charging current when the battery is at a low state of charge and tapering the current to lower rates as the battery becomes more fully charged.

Temperature Cutoff (TCO):

A protective or safety device (e.g., thermostat, PTC, etc.) which senses temperature in a battery and opens or cuts off the electrical circuit if the specified temperature is exceeded, thus preventing a further rise in temperature due to the charge or discharge of a battery. 


A device at the end of a cell or wire for making a connection to an adjoining cell or wire. 


The parts of a battery to which the external electric circuit is connected.

Thermal Fuse:

a one-time, non-resettable fuse used to protect against over-current Thermal runaway — A critical condition arising during constant voltage charging in which the current and the temperature of the battery produce a cumulative mutually-reinforcing effect which further increases them and can lead to the destruction of the battery.

Thermal runaway:

A critical condition arising during constant voltage charging in which the current and the temperature of the battery produce a cumulative mutually-reinforcing effect which further increases them and can lead to the destruction of the battery.


temperature sensing device, used to measure the temperature of a battery pack or cell. Typically a Negative Temperature Coefficient (NTC) device. Exhibits a predictable and precise decrease in resistance with an increase in temperature


circuit protection device used to prevent over-current and over-temperature. A thermostat will go from a low-resistance state to an open circuit at a predetermined temperature

Thionyl Chloride Lithium:

offer extremely long service life (15 to 20 years) and low self-discharge rates. Ideal for applications with low continuous-current or moderate pulse-current requirements, and applications where physical access is limited. Highest energy density of all lithium types. Manufactured in welded, hermetically sealed cases in cylindrical, coin, and wafer types

Three phase zone:

The area where 3 phases (gas, liquid, and solid) contact with each other, Reactions of substances composing these 3 phases take place easily.

Time Charge:

a charging method, terminated after a predetermined amount of time, designed to charge a battery or cell within 6 to 16 hours

Top-Off Charge:

charge step designed to fully charge a battery or cell when a rapid or fast charge termination that does not reach 100% SOC is used. Most commonly used after a dT/dt termination


movement of ions within a cell. Cations carry net-positive charges; anions carry net-negative charges

Trickle Charge:

A charge at a low rate, balancing losses through local action and/or periodic discharge, to maintain a cell or battery in a fully charged condition. 



Valve Regulated Lead-Acid (VRLA) Battery:

Battery that is sealed and maintenance-free. 


Mechanisms that allow gases to escape from the battery while retaining the electrolyte within the case. Flame-arresting vents typically contain porous disks that reduce the probability of an internal explosion as a result of an external spark. Vents come in both permanently fixed and removable designs. 


The unit of measurement of electromotive force, or difference of potential, which will cause a current of one ampere to flow through a resistance of one ohm. Named for Italian physicist Alessandro Volta (1745-1827).

Voltage Cutoff:

electronics board which disconnect the load from a battery pack

Voltage delay:

During open circuit storage, some battery systems develop a passivation film on the surface of the active material. On the initial discharge, these batteries may momentarily demonstrate a lower than normal voltage until this film is removed by the discharge.

Voltage Depression:

An abnormal drop in voltage below expected values during the discharge of a battery. 

Voltage Drop:

The net difference in the electrical potential (voltage) when measured across resistance or impedance (ohms). Its relationship to current is described in Ohm’s law. 

Voltage limit:

A voltage value a battery is not permitted to rise above on charge and/or fall below on discharge.

Voltage Regulator:

A device that regulates the output of a generator or alternator by controlling the current and voltage. 

Voltage Reversal:

The changing of the normal polarity of a battery due to overdischarge. 


A system that incorporates a mechanical identifier on batteries and devices to ensure only batteries of the correct voltage are connected to the device. 

Voltage-limiting charger:

A charger that limits the maximum voltage to a battery but allows the current to drop while maintaining the voltage limit. A voltage limiting charge normally also includes current limiting. (Typically used on SLA and Li-ion chargers).

Voltage, cutoff:

Voltage at the end of useful discharge. (See Voltage, end-point.)

Voltage, end-point:

Cell voltage below which the connected equipment will not operate or below which operation is not recommended.

Voltage, nominal:

Voltage of a fully charged cell when delivering rated current.


A unit of measuring electrical pressure, all batteries are rated in volts DC (Direct Current). 


An electronic device used to measure voltage, normally in a digital format. 

Volumetric Energy Density:

ratio of a cell's energy to its total volume. Usually expressed in Watt-hours per liter (Wh/l). Also called "power density"


Valve-regulated lead-acid battery. AGM and gel are the two types of VRLA batteries. These batteries have no “free” liquid electrolyte and in the cell operate on the oxygen recombination cycle, which is designed to minimize water loss. VRLA batteries feature vents that are one-way burp valves. These low-pressure burp valves prohibit air ingress to the cell while permitting gases to vent from the cell if necessary. The pressure maintained in the battery, though only very slight (<3-psi) is required to facilitate the oxygen generated at the positive plates back into water. 


Wall-less Design:

A battery design where the structural support for the cells is formed by an open plastic framework. 


A measurement of total power. It is amperes multiplied by volts. 120 volt @ 1 amp = 12 volts @ 10 amps.

Watt Hours (Wh):

amount of electric energy that can be withdrawn from a battery or cell under specified conditions. This energy is measured in milli-Watt-hours (mWh). Product of the discharge voltage, discharge rate, and discharge time

Wet Cell:

A cell, the electrolyte of which is in liquid form and free to flow and move.

Working Voltage:

voltage range of a battery or cell during discharge





A primary battery (non-rechargeable) that was commonly used for applications such as watches and hearing aids. In relation to their physical size, Zinc/Air batteries store more energy per unit of weight (in terms of 220 W h/kg) than any other primary type.