A rechargeable battery or cell.


A proton donor. A compound containing hydrogen which dissociates in aqueous solution producing positively charged hydrogen ions (H+). An acidic solution has a pH less than 7.0.

Active Material

The chemically reactive materials in an energy cell which react with each other converting from one chemical composition to another while generating electrical energy or accepting electric current from an external circuit.

Actual Battery 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.


Permanent loss of capacity with frequent use or the passage of time due to unwanted irreversible chemical reactions in the cell.

AGM (Absorbtive Glass Mat) battery

A lead acid battery using a glass mat to promote recombination of the gases produced by the charging process.

Air Cell

Battery system which utilizes oxygen in combination with catalyzed carbon as the cathode and zinc as the anode to produce electricity.


A compound which dissolves in water producing negatively charged hydroxide ions. Alkaline solutions are strongly basic and neutralise acids forming a salt and water.

Alkaline Battery

A battery which uses an aqueous alkaline solution for its electrolyte.

Ambient Temperature

The average temperature surrounding the battery, typically air temperature.


Without definite shape or structure, without crystalline structure.

Amp Hour or Ampere-Hour

A unit of measurement of a battery’s electrical storage capacity. Current multiplied by time in hours equals ampere-hours. One amp hour is equal to a current of one ampere flowing for one hour. Also, 1 amp hour is equal to 1,000 mAh.

Ampere or Amp

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 Capacity

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

Ampoule Battery

A battery in which the electrolyte is stored in a separate chamber from the cell electrodes until the battery is needed.

Anechoic Chamber

A room whose walls do not reflect either electromagnetic or acoustic waves.


Particles in the electrolyte of a galvanic cell carrying a negative charge and moving toward the anode during operation of the cell.


Showing differences of property or of effect in different directions.


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.


The American National Standards Institute publish standards for batteries jointly with NEMA.

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.

Aqueous Solution

Chemical components in liquid or gel form.

Arrhenius Equation

The relationship between the rate at which a chemical reaction proceeds and its temperature. In general terms, heat speeds up the chemical action.


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 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.

Battery Charge Rate

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

Battery Charger

A device capable of supplying electrical energy to a battery.

Battery Management System (BMS)

Electronic circuits designed to monitor the battery and keep it within its specified operating conditions and to protect it from abuse during both charging and discharging.

Battery Monitoring

Battery monitoring circuits monitor the key operating parameters (current, voltage, temperature, SOC, etc.) of the battery and provide information to the user.


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


To do something seemingly impossible using only the available resources. In the context of DC battery power circuits it means generating a DC voltage higher than the battery voltage.

Butler Volmer equation

Used by cell designers to predict the current which will flow in a battery. It is the sum of the anodic and cathodic contributions and is directly proportional to the surface area of the electrodes, increasing exponentially with temperature.

Button cell

Miniature cylindrical cell with a characteristic disc shape.

Calendar life

The expected life time duration of a cell whether it is active use or in storage.

Capacity Offset

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


Cathode 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, the negative electrode of the cell is the cathode.


The CE marking indicates that the product has been designed and manufactured in conformity with the essential requirements of all relevant EU directives, and submitted to the relevant conformity assessment procedure.


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 Reversal

Reversing polarity of terminals of a cell or battery due to over discharge.


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

Charge acceptance

The ability of a secondary cell to convert the active material to a dischargeable form. A charge acceptance of 90% means that only 90% of the energy can become available for useful output. Also called Coulombic Efficiency or Charge Efficiency.

Charge efficiency

The ratio (expressed as a percentage) between the energy removed from a battery during discharge compared with the energy used during charging to restore the original capacity. Also called the Coulombic Efficiency or Charge Acceptance. See alternative definition above.

Charge Rate

The amount of current applied to battery during the charging process. This rate is commonly expressed as a fraction of the capacity of the battery. For example, the C/2 or C/5.

Charge retention

The ability of a battery to retain its charge in zero current conditions. Charge retention is much poorer at high temperatures.


The proce
ss of supplying electrical energy for conversion to stored chemical energy.

Constant-Current Charge

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

Constant-Voltage Charge

A charging process in which the voltage applied to a battery is held at a constant value.

Coulombic Efficiency

The ratio (expressed as a percentage) between the energy removed from a battery during discharge compared with the energy used during charging to restore the original capacity. Also called Charge Efficiency or Charge Acceptance.


C is a value which expresses the rated current capacity of a cell or battery. A cell discharging at the C rate will deliver its nominal rated capacity for 1 hour. Charging and discharging currents are generally expressed as multiples of C. The time to discharge a battery is inversely proportional to the discharge rate.

Cutoff Voltage

The prescribed lower-limit voltage at which battery discharge is considered complete. The cutoff 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.


One sequence of charge and discharge.

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.

Deep Cycle

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

Deep Discharge

Withdrawal of all electrical energy to the end-point voltage before the cell or battery is recharged.

Depth of Discharge

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.

Direct Current (DC)

The type of electrical current that a battery can supply. One terminal is always positive and another is always negative.


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


Withdrawal of current from a cell.

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 Leclanche 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 load current or power a battery is expected to supply for specified time periods.

Electrochemical Couple

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


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.

Electromotive Force EMF

The ability of an electrical source to deliver energy. It is the difference of potentials which exists between the two electrodes of opposite polarity in an electrochemical cell. Also known as the Cell voltage.


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.

End-of-Discharge Voltage

The voltage of the battery at termination of a discharge.


Describes a chemical action in which heat is absorbed.

End-Point Voltage

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

Energy Density

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


The amount of energy released or absorbed by a chemical reaction. The “Free Enthalpy” (also called the “Change in Gibbs Free Energy”) in a reaction is the maximum amount of chemical energy available from a system that can be converted into electrical or mechanical energy and vice versa. (discharge and charge respectively).


The process of bringing every cell in a battery chain to the same state of charge (SOC)


Describes a chemical action in which heat is produced.

Final Voltage

Final voltage is same as 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.

Fuel Cell

An electrochemical generator in which the reactants are stored externally and may be supplied continuously to a cell.

Functional End Point (FEP)

Voltage below which battery-operated equipment will not function properly.

Galvanic Cell

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

Gravimetric Energy Density (Wh/Kg)

The energy output per unit weight of a battery.

Gravimetric Power Density (W/Kg)

The power output per unit weight of a battery.

High-Rate Discharge

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.

Horse Power (Hp)

The rate of doing work. 1 Hp = 746 Watts or 550 foot pounds per second.


The amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature; the ratio of the actual water vapor pressure to the saturation vapor pressure.

Hybrid Electric Vehicle (HEV)

A vehicle which has two forms of motive power, one of which is electric.


A device used for measuring the specific gravity of a fluid. In the case of lead acid batteries the specific gravity provides a measure of the state of charge of the cell.


An instrument for measuring humidity. Often confused with a hydrometer.

Internal Resistance

The resistance to the flow of an electric current within the cell or battery.


The escape of electrolyte to the outer surface of the bat
tery or cell.

Leclanche Cell

A zinc carbon or zinc chloride cell. It is a dry cell.

Lifetime Energy Throughput

The total amount of energy in Watthours which can be taken out of a rechargeable battery over all the cycles in its lifetime before its capacity reduces to 80% of its initial capacity when new.

Linear charger

Charger which uses a linear regulator.

Lithium Ion Cell

A secondary lithium cell in which both the negative and positive electrodes are lithium insertion (intercalation) compounds. Also known as rocking chair, shuttlecock or swing cell.

Lithium Polymer Cell

A lithium ion cell with a solid polymer electrolyte.

Load current

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

Low-Rate Discharge

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

Memory Effect

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.


Very small battery built using nano technology. Of microscopic size 1 micron diameter they deliver 3.5 volts. The electrodes are ceramic or carbon particles and the electrolyte is a solid polymer impregnated in an aluminium oxide membrane.

Negative Delta Voltage (NDV)

The NDV is the drop in the battery voltage which occurs when NiCad or NiMH cells reaches their fully charge state. Used to detect the end of the charging cycle in Nicads.

Negative Terminal

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


The National Electric Manufacturers Association in the USA publish standards for batteries jointly with ANSI.

Nominal Voltage

Voltage of a fully charged cell when delivering rated current.

Nonaqueous Batteries

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


Non-Recurring Engineering costs. A one time charge for design and implementation of custom battery packs or other products.

Ohmic Loss

The voltage drop across the cell during passage of current due to the internal resistance of the cell.

Open Circuit

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

Open-Circuit Voltage

The difference in potential between the terminals of a cell when the circuit is open (i.e., a no-load condition).


Continuous charging of the battery after it reaches full charge. Generally overcharging will have a harmful influence on the performance of the battery which could lead to unsafe conditions. It should therefore be avoided.


Exceeding the manufacturer’s recommended maximum discharge current for a cell or battery.


Discharging a battery below the end voltage or cut-off voltage specified for the battery.


The difference between the actual potential at which an electrochemical reaction occurs, and its theoretical equilibrium potential.


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

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.

Passivation Layer

A resistive layer that forms on the electrodes in some cells after prolonged storage impeding the chemical reaction. This barrier must be removed to enable proper operation of the cell. Applying charge/discharge cycles often helps in preparing the battery for use. In other applications, passivation is used as a method of shielding a metal surface from attack.

Permanent Charge

The charging current which can safely be continuously supported by the battery, regardless of the state of the charge.

Peukert’s Equation

An empirical formula that approximates how the available capacity of a battery changes according to the rate of discharge. The equation shows that at higher currents, there is less available energy in the battery.

Photovoltaic Cell

A device that directly converts the energy in light into electrical energy. Also called a photocell, a solar cell or a PV cell.

Photovoltaic Effect

The generation of an electromotive force as a consequence of the absorption of radiation. In practice a current which flows across the junction of two dissimilar materials when light falls upon it.

Pilot Cell

A selected cell whose condition is assumed to indicate the condition of the entire battery.


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

Positive Terminal

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

Pouch Cell

A battery or cell contained in a flexible metal foil pouch.


The standard proposed for next generation of automotive batteries. Nominally 42 Volt systems.

Primary Battery

A battery made up of primary cells.

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

A slim rectangular sealed cell in a metal case. The positive and negative plates are stacked usually in a rectangular shape rather than rolled in a spiral as done in a cylindrical cell.


A facility incorporated into battery packs to protect the cells from out of tolerance working conditions or misuse.

Pulse Charger

Versatile, hybrid charger having some of the advantages of both switch-mode and linear chargers. More costly than both.

Pulse Discharge

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

Quick Charge

Charging in three to six hours at about 0.3C rate. Needs special charger.

Quiescent Current

The current which continues to be drawn from the battery when the application it powers is in standby or hibernation mode.

RAM Cells

Rechargeable Alkaline Manganese cells.

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, which refers to secondary cells or batteries.


State in which the gases normally formed within the battery cell during its operation, are recombined to form water.


Reclamation of materials without endangering human health and the environment.

Redox Battery

A battery in which the chemical energy is stored in two dissolved ionic reactants separated by a membrane.


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

Remote-Area Power Supplies (RAPS)

Power systems deriving their energy from local solar or wind sources using a battery for energy storage and supplying the load through DC-DC converters or AC inverters.

Reserve Battery

Batteries which are stored in an inactive state without their electrolyte. They are only activated when needed by the introduction of the electrolyte.

Resettable F

A fuse which protects against excessive current and temperature by interrupting the flow of current. After opening it will reset after the fault conditions have been removed but only after it has cooled. It requires no manual resetting or replacement. The “Polyswitch” is an example of this.

Rocking Chair Cell

A lithium ion cell


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).

Secondary Battery

A battery made up of secondary or storage cells.

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.

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.

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

For a dry cell, the period of time (measured from date of manufacture), at a storage temperature of 21 degrees C (69 degrees F), after which the cell retains a specified percentage (usually 90%) of its original energy content.

Short-Circuit Current

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


A condition that occurs when a short electrical path is unintentionally created. Batteries can supply hundreds of amps if short-circuited, potentially melting the terminals and creating sparks.

Shuttlecock Cell

A lithium ion cell.


Heating a mixture of powdered metals, sometimes under pressure, to the melting-point of the metal in the mixture which has the lowest melting-point, the melted metal binding together the harder particles.

SLA Battery

Sealed Lead Acid battery. In sealed batteries the generated oxygen combines chemically with the lead and then the hydrogen at the negative electrode, and then again with reactive agents in the electrolyte, to recreate water. A recombinant system. The net result is no significant loss of water from the cell.

SLI Battery

Common automotive battery used for Starting Lighting and Ignition.

Smart Battery

An intelligent battery which contains information about its specification, its status and its usage profile which can be read by its charger or the application in which it is used.

Solar Cell

A photovoltaic cell. Solar cells convert sunlight energy into electric current. They do not store energy.

Solid State Battery

Cells with solid electrolytes. Lithium polymer cells are examples of this technology.

Starting-Lighting-Ignition (SLI) Battery

A battery designed to start internal combustion engines and to power the electrical systems in automobiles when the engine is not running. SLI batteries can be used in emergency lighting situations.

Stationary Battery

A secondary battery designed for use in a fixed location.


The branch of chemistry that deals with the numerical proportions in which substances react.

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.

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.


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

Tafel Equation

The relationship between the internal electrode potentials in a battery and the current which flows. This is an exponential relationship based on empirical results which quantifies the elecrochemical reactions. It is analogous to the Arrhenius equation which quantifies the thermochemical process relating the temperature to the rate at which a chemical action progresses.

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. In quick chargers the charging current is is progressively reduced in a controlled way by controlling the supply voltage. In slow chargers the voltage is fixed and the charging current reduces in an uncontrolled way due to increase in the cell voltage as the charge builds up.


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

Thermal Imaging

photographic technique which displays the range of temperatures of a warm body in the form of a colour spectrum. Used as a design verification tool for detecting hot spots in battery and other equipment designs.

Thermal Management

The means by which a battery is maintained within its operating temperature limits during charging and discharging.

Thermal Runaway

A condition whereby a cell on charge or discharge will destroy itself through internal heat generation caused by high overcharge or high rate of discharge or other abusive conditions.

Traction Battery

A high power deep cycle secondary battery designed to power electric vehicles or heavy mobile equipment.

Trickle Charge

A continuous charge at low rate, balancing losses through local action and/or periodic discharge, to maintain a cell or battery in a fully charged condition. Normally at a C/20 to C/30 rate.

Trickle Charging

A method of recharging in which a secondary cell is either continuously or intermittently connected to a constant-current supply that maintains the cell in fully charged condition.


A normally sealed mechanism that allows for the controlled escape of gases from within a cell.


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).

Voltaic Efficiency

The ratio (expressed as a percentage) between the voltage necessary to charge a secondary cell and the corresponding discharge voltage.


A measurement of total power. It is current multiplied by voltage (amperes multiplied by volts).

Wet Cell

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


A desperation measure to revive a shorted cell suffering from dendrites. A very high current, low voltage pulse from a large capacitor used in an attempt to vaporise the dendrites.

Zebra battery

A high temperature Sodium Nickel Chloride battery delivering high power.