Document No. 5-0324 Rev G
Rated C1 capacity - The rated capacity, expressed in Ampere-hours (Ah), obtained from a
fully charged battery when discharged at the C1 rate to the specified end point voltage at a
temperature of 21 - 25C (70 - 77F).
Self discharge - The decrease in the state of charge of a battery, over a period of time, due
to internal electrochemical losses. The self-discharge rate accelerates as the temperature
increases and as the battery ages.
Separator - A porous, insulating material placed between plates of opposite polarities to
prevent internal short circuits.
Series connection - A circuit in which battery terminals of opposite polarity are connected
together. The voltage of each battery adds together while capacity remains the same.
Specific gravity (S.G.) - The weight of the electrolyte as compared to the weight of an
equal volume of pure water, used to measure the strength or percentage of sulfuric acid in
the electrolyte.
State of charge (SOC) - The ratio of available capacity in a battery to its fully charged
capacity. Example: Battery A is discharged and gives 32 Ah of capacity to its EPV. After a
full charge, it is discharged again and gives 40 Ah. The SOC of Battery A before the first
discharge was 32/40 = 80%. Note that the SOC does not represent the battery’s capacity as
a percentage of its rated capacity and should not be used to determine airworthiness (See
State of Health).
State of health (SOH) - The ratio of available capacity in a battery when fully charged to its
rated capacity. Example: Battery B is fully charged and gives 38 Ah capacity to its EPV.
Battery B is rated at 42 Ah. The SOH of battery B is 38/42 = 90%. The SOH is measured
when a capacity test is performed and is used to determine the battery’s airworthiness.
Sulfation - Refers to the formation of lead sulfate within the battery plates when a battery is
discharged. If the battery remains discharged, the lead sulfate becomes more resistive
which can limit or prevent the recharging of the battery. Sulfated batteries may sometimes
be recovered with a special conditioning charge.
Valve regulated lead-acid (VRLA) battery -
A lead-acid battery in which the internal
pressure is regulated by a pressure relief valve and pressure build-up is minimized
by internal recombination of gases formed during the charging process. A VRLA
battery requires no maintenance of the liquid level which is necessary in some types
of flooded lead-acid batteries.
Valve regulated sealed lead-acid (VRSLA) battery – An alternate terminology for a VRLA
battery (see definition above).
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