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Technical Glossary


Active material

Material which reacts chemically to produce electric energy when the cell discharges.


By convention, cell electrode at which an oxidation reaction occurs.


One or more cells fitted with devices necessary for use, for example case, terminals, marking and protective devices.

Battery on float (charge)

Secondary battery whose terminals are permanently connected to a source of constant voltage sufficient to maintain the battery approximately fully charged, and which is intended to supply power to an electric circuit, if the normal supply is temporarily interrupted.

Battery rack

Support, stand or grating with one or more levels or tiers for the installation of cells or monobloc containers in a stationary battery.

Boost charge

  Accelerated charge applied at greater than normal values of electric currents or of voltages (for a particular design) during a short time interval.


Electric charge which a cell or battery can deliver under specified discharge conditions.


Container for the plate pack or packs and electrolyte of a cell or cells made of a material impervious to the electrolyte.


By convention, cell electrode at which, a reduction reaction occurs.


Basic functional unit, consisting of an assembly of electrodes, electrolyte, container, terminals and usually separators, that is a source of electric energy obtained by direct conversion of chemical energy.

Cell reversal

Reversing of the polarities of the electrodes of a cell, generally due to over-discharge of a low capacity cell in a series arrangement.

Charge acceptance

  Ability of a secondary battery to increase its state of charge under specified conditions.

Charge efficiency

  Ratio of the electric charge discharged from a secondary battery to the electric charge provided during the preceding charge.

Charge factor

  Factor by which the quantity of electricity on discharge has to be multiplied to determine the quantity of electricity on charge required for the battery to recover its original state of charge.

Charge rate

  Electric current at which a secondary cell or battery is charged. NOTE: The charge rate is expressed as the reference current It = Cn/n where Cn is the rated capacity declared by the manufacturer and n is the time base in hours for which the rated capacity is declared.

Charge retention Capacity retention

  Ability of a cell or battery to retain capacity on open circuit under specified conditions.


  Conductor of electricity used for carrying current between components in an electric circuit.

Constant current charge

  Charge during which the electric current is maintained at a constant value regardless of the battery voltage or temperature.

Constant voltage charge

  Charge during which the voltage is maintained at a constant value regardless of charge current or temperature.


  Set of operations that is carried out on a secondary cell or battery and is regularly in the same sequence. NOTE: In a secondary battery these operations may consist of a sequence of a discharge followed by a charge or a charge followed by a discharge under specified conditions. This sequence may include rest periods.

Depth of discharge (DOD)

  Capacity discharged from a battery in relation to the rated capacity. Frequently expressed as a percentage, e.g. 60% DOD.


  Operation by which a battery delivers, to an external electric circuit and under specified conditions, electric energy produced in the cells.

Discharge current

  Electric current delivered by a battery during its discharge.

Discharge rate

  The value of the current in amperes at which a battery is discharged expressed as a fraction or multiple of the rated capacity in ampere hours of the cell, e.g. It/5 (C/5) or 5It (5C).

Discharge voltage

  Voltage between the terminals of a cell or battery when being discharged.


  Liquid or solid substance containing mobile ions which render it ionically conductive.

Energy density

  The energy output delivered per unit of volume or weight of a cell, e.g. watt hours per dm³ (Wh/dm³), watt hours per kg (Wh/kg).

Energy efficiency

  Ratio of the electric energy provided from a secondary battery during discharge to the electric energy supplied to the battery during the preceding charge.

Equalization charge

  Extended charge to ensure an equal state of charge of all cells in a battery.

Final voltage / Cut-off voltage

  Specified voltage of a battery at which the battery discharge is terminated.

Flame arrester vent

Vent of special design which provides protection against the propagation of a flame front from or into the interior of a secondary cell. NOTE: This flame front may originate from a spark or an external naked flame igniting combustible electrolysis gas.

Gassing of a cell

  Evolution of gas resulting from electrolysis of the water in the electrolyte of a cell.

Internal apparent resistance

  Quotient of change of voltage of a battery by the corresponding change in discharge current under specified conditions.

Lead acid battery

  Secondary battery with an aqueous electrolyte based on dilute sulphuric acid, a positive electrode of lead dioxide and a negative electrode of lead

Maintenance-free battery

  Secondary battery which, during the service life, requires no maintenance provided specified operating conditions are fulfilled.

Modified constant voltage charge

  Constant voltage charge where the electric current is limited to a predetermined value.

Negative plate

  Cell component containing active material at which, by convention, an oxidation reaction occurs during discharge.

Nickel cadmium battery

  Secondary battery with an alkaline electrolyte, a positive electrode containing nickel oxide and a negative electrode of cadmium.

Nominal voltage

  Suitable approximate value of the voltage used to designate or identify a cell, a battery or an electrochemical system. The nominal voltage of a nickel-cadmium cell is 1.2 V and for Lead-Acid 2.0 V.

Open-circuit voltage

  Voltage of a cell or battery when the discharge current is zero.

Parallel connection

  Arrangement of cells or batteries wherein all the positive terminals and all the negative terminals, respectively, are connected together.

Pocket plate

  Plate of a nickel-cadmium or nickel-iron cell consisting of an assembly of perforated steel pockets, which may be nickel plated, and which contain the active material.

Positive plate

  Cell component containing active material at which, by convention, a reduction reaction occurs during discharge.

Primary cell

  Cell which is not be electrically recharged.

Rated capacity

  Quantity of electricity C5Ah (ampere-hours) declared by the manufacturer which a single cell can deliver when discharged at reference test current of 0.2It A to a final voltage of 1.0 V at +20°C after charging, storing and discharging under specified conditions.

Safety vent

  Vent of special design which allows to release gas from a secondary cell in order to avoid excessive internal pressure and thereby to preclude rupture of the cell container.

Sealed cell

  Cell which remains closed and does not release either gas or liquid when within the limits specified by the manufacturer. NOTE: A sealed cell may be equipped with a safety device to prevent a dangerously high internal pressure and is designed to operate during its life in its original sealed state.

Secondary cell

  Cell which is designed to be electrically recharged.


  Phenomenon by which a cell or battery loses energy in other ways than by into an external circuit.


  Component of a cell, made up of material permeable for ions, which prevents electric contact between cell plates of opposite polarity within a cell.

Series connection

  Arrangement of cells or batteries wherein the positive terminal of each cell or battery is connected to the negative terminal of the next cell or battery in sequence.

Service life

  Total period of useful life of a cell or a battery in operation.

Single level charge

  Charging method applied to a secondary battery using a single rate floating voltage.

Sintered plate

Plate of an alkaline secondary cell the support of which is made by sintering metal powder and into which the active material is introduced.


  Conductive part of a device, electric or electric network, provided for connecting that device, electric circuit or electric network to one or more external conductors.

Thermal runaway

  Unstable condition arising during constant voltage charge in which the rate of heat dissipation capability, causing a continuous temperature increase with resulting further charge current increase, which can lead to the destruction of the battery.

Trickle charge

  Method of charge applied to a battery wherein the state of charge is maintained by a continuous, long term, regulated small electric current.

Two level charge Two srep charge

  Charging method applied to a secondary battery using two levels of charge rate with feedback control to initiate the changeover from a high to a low charge rate.


  Component of a cell which permits the flow of gas in one direction only.

Valve regulated lead acid battery (VRLA)

  Secondary battery in which cells are closed but have a valve which allows the escape of gas if the internal pressure exceeds a predetermined value. NOTE: The cell or battery cannot normally receive additions to the electrolyte.

Vent cap

  component fitted into the filling hole of a cell with a provision of allowing the venting of electrolysis gas from the cell.

Vented cell

  Secondary cell having a cover provided with an opening through which products of electrolysis and evaporation are allowed to escape freely from the cell to the atmosphere.


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