Document No. 5-0324 Rev G
End of life - The stage at which the battery or cell meets specific failure criteria.
End point voltage (EPV) - The voltage at which the discharge current is terminated when
measuring battery capacity. Sometimes called cutoff voltage or voltage end point. Unless
otherwise stated, the EPV is equal to 20.0 volts for 24-volt aircraft batteries (10.0 volts for
12-volt batteries).
Float charge - A method of maintaining a cell or battery in a charged condition by
continuous, long term constant voltage charging at a level sufficient to balance self
discharge.
Gassing - The evolution of gas from one or more of the electrodes in a cell when the battery
reaches full charge.
Internal impedance - The electrical impedance inside the battery that restricts the flow of
current during charging and discharging. The internal impedance depends on the size of
the battery, state of charge, temperature and age.
Ipp/Ipr – The Ipp is the peak power current, defined as the current which the battery delivers
at 0.3 seconds during a constant voltage discharge equal to half of the nominal voltage. The
Ipr is the power rating, defined as the current which the battery delivers at 15 seconds
during a constant voltage discharge equal to half of the nominal voltage.
Lead acid - Term used in conjunction with a battery that utilizes lead and lead dioxide as
the active plate materials in a diluted electrolyte solution of sulfuric acid and water. Nominal
cell voltage is 2 volts.
Lead dioxide – The oxide of lead present in charged positive plates (PbO
2
) and is
sometimes 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.
Load tester - An instrument which measures the battery voltage with an electrical load on
the battery to determine its overall condition.
Nominal voltage – The nominal cell voltage (2 volts for a lead-acid cell) multiplied by the
number of cells in series within the battery. The nominal voltage of a 6-cell battery is 12 volts
and that of a 12-cell battery is 24 volts.
Open circuit voltage (OCV) - The voltage of the battery at rest (no charging or discharging
current present). A stable OCV requires a rest of at least four hours.
Overcharge – Applying excessive voltage to force current through a cell after all the active
material has been converted to the charged state. The result is decomposition of water in
the electrolyte into hydrogen and oxygen gas and accelerated grid corrosion.
Oxygen recombination - The process by which oxygen generated at the positive plate
during charge reacts with the pure lead material of the negative plate to reform water.
Parallel connection - A circuit in which battery terminals of like polarity are connected
together. The capacity of each battery adds together while voltage remains the same.
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