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Term Definition
Duty Cycle

The conditions and usage to which a battery is subjected during operation, consisting of charge, overcharge, and discharge.


Conducting body in which active materials are placed and through which current enters or leaves cell.


In a lead-acid battery, the electrolyte is sulfuric acid diluted with water. It is a conductor and is also a supplier of hydrogen and sulfate ions for the reaction.

Electromotive Force (EMF)

Potential causing electricity to flow in a closed circuit.


That part of an atom having a negative charge.

End Of Discharge Voltage

The voltage of the battery at the termination of a discharge but before the discharge is stopped. See End Point Voltage (EPV).

End Of Life

The stage at which the battery or cell meet specific failure criteria.

End Point Voltage

Cell or battery voltage at which point the rated discharge capacity had been delivered at a specified rate-of-discharge. Also used to specify the cell or battery voltage below which the connected equipment will not operate or below which operation is not recommended. Sometimes called cutoff voltage or voltage end point.


Cell or battery output capability, expressed as capacity times voltage, or watt-hours (W-hr).

Energy Conversion

The change from chemical to electrical energy with the cell, or the reverse.

Energy Density

The ratio of cell or battery energy to either the weight (Wh/lb or Wh/kg) or the volume (Wh/L or Wh/cu.in.).


The process whereby gases generated in the cell carry electrolyte through the vent cap.

Environmental Conditions

External circumstances to which a cell or battery may be subjected, such as ambient temperature, humidity, shock, vibration and altitude.


See Reconditioning.

Equalization Charge

A maintenance procedure consisting of a sustained constant current charge used to correct cell imbalance.

External Power

A device that is used to supply electrical power via a cable and plug to the airframe external power receptacle. External power is used to prevent the aircraft batteries from being discharged during maintenance or often used for electrical power during engine starting. Some airframe external power electrical systems are designed to bypass the battery buss to prevent the batteries from being overcharged. To prevent the batteries from being overcharged, we recommend that the batteries be disconnected if the airframe external power electrical system design does not bypass the battery buss when external power is on in excess of four hours. External power should not be set higher than 2.38 volts per cell, 14.2 for 12 volt batteries and 28.5 DCV for 24 volt batteries.

Failure, Functional

Condition in which the battery has caused the end-use device to fail to function at the performance level expected.

Failure, Permanent

A condition which does not permit a cell or battery to be reconditioned or restored to an acceptable performance level.

Failure, Reversible

Failure condition which may be corrected through the application of certain electrical procedures.

Fast charging

Rapid return of energy to a battery at the C rate or more.

Float charge

A method of maintaining a cell or battery in a charged condition by continuous, long-term, constant voltage charging at level sufficient to balance self-discharge.

Flooded cell

A cell design which incorporates an excess amount of electrolyte, also see Vented Cell.


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.


In aircraft use, the result of attaching one battery cable to the body or airframe which is used as a path for completing a circuit in lieu of a direct wire from a component.

High Rate Discharge

Withdrawal of large amounts of current for short intervals of time from a cell or battery, usually at a rate that will completely discharge a cell or battery in less than 1 hour.


A float type instrument used to determine the state-of-charge of a battery by measuring the specific gravity of the electrolyte (i.e. the amount of sulfuric acid in the electrolyte).

Internal Impedance

The opposition to the flow of an alternating current at a particular frequency in a cell or battery at a specified state-of-charge and temperature.

Internal Resistance

The opposition or resistance to the flow of a direct electric current within a cell or battery; the sum of the ionic and electronic resistance of the cell components. Its value may vary with the current, state-of-charge, temperature, and age. With an extremely heavy load, such as an engine starter, the cell voltage may drop to approximately 1.6. This voltage drop is due to the internal resistance of the cell. A cell that is partly discharged has a higher internal resistance than a fully charged cell, hence it will have a greater voltage drop under the same load. This internal resistance is due to the accumulation of lead sulfate on the plates. The lead sulfate reduces the amount of active material exposed to the electrolyte, hence it deters the chemical action and interferes with the current flow.


Part of a molecule or group of atoms, positively or negatively charged, which transports electricity through the electrolyte.


Unit of energy, equal to a watt/second (newton/meter).

Lead Acid

Terms used in conjunction with a cell or battery that utilizes lead and lead peroxide as the active plate materials in a diluted electrolyte solution of sulfuric acid and water. Nominal cell voltage about 2.1 volts.

Lead Dioxide

A higher oxide of lead present in charged positive plates and frequently referred to as lead peroxide.

Lead Sulfate

A lead salt formed by the action of sulfuric acid on lead oxide during paste mixing and formation. It is also formed electrochemically when a battery is discharged.


The duration of satisfactory performance, measured as usage in years or as the number of charge/discharge cycles.

Lithium Ion Aircraft Battery

Main aircraft battery built with safest chemistry in Lithium ion batteries, a cathode material of lithium iron phosphate which inhibits oxygen generation. Lithium ion aircraft batteries must be integrated into the control software and electronics of the aircraft system with redundant built in safety features.

Load Tester

An instrument which measures the battery voltage with an electrical load on the battery to determine its overall condition and its ability to perform under engine starting conditions or essential power requirements.

Low Rate Discharge

Withdrawal of small amounts of current for long periods of time from a cell or battery, usually longer than 1 hour.


The care and procedures necessary to keep a battery in usable condition, such as reconditioning and water addition to electrolyte of a vented cell.


A portion of the battery case enclosing the vent caps or vent valves. Sometimes with ports that can be connected overboard for ventilation.

Manufacturing Variations

Differences in performance characteristics between products of the same design, attributable to process deviations within expected tolerances.


Directed movement of an ion of the electrolyte under the influence of an electric field.

Negative Electrode

See Negative Plate.

Negative Plate

The plate which has an electrical potential below that of the other plate during normal call operation.

Nominal Capacity

A designation by the battery manufacturer which helps identify a particular cell model and also provides an approximation of capacity; usually expressed in ampere-hours at a given discharge current.

Nominal Voltage

Voltage of a fully charged cell or battery when delivering rated capacity at a specified discharge rate.

Open Circuit Voltage

The voltage of a battery when it is not delivering or receiving power.


The forcing of current through a cell after all the active material has been converted to the charged state. In other words, charging continued after 100% state-of-charge is achieved. The result will be the decomposition of water in the electrolyte into hydrogen and oxygen gas.

Oxygen recombination

The process by which oxygen generated at the positive plate during charge reacts with the pure lead material of the negative plate and in the presence of sulfuric acid and reforms water.

Parallel connection

A circuit in which battery poles of like polarity are connected to a common conductor.


A grid or framework that gives mechanical support to the active materials of a cell. The combination is termed an electrode.


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