Document No. 5-0324 Rev G
H. Cold Weather Operation:
In cold climates, the state of charge of the battery should be kept at a maximum to
prevent freezing of the electrolyte. A fully charged battery will not freeze even under
the coldest weather conditions, but a discharged battery will freeze even when
moderately cold. Table 3 gives the freezing point of electrolyte at various states of
charge.
Frozen batteries are not capable of charging or discharging except at very low rates,
and may be permanently damaged by expansion of the electrolyte. If a battery
becomes frozen, it should be thawed by placing it at room temperature for at least
24 hours, and then serviced in accordance with the applicable CMM. However, if the
battery container has any evidence of cracking, the battery is no longer serviceable
and should not be used.
Operating an aircraft battery in cold weather is equivalent to using a battery of lower
capacity. For example, a fully charged battery at 25°C (77°F) may be capable of
starting an engine twenty times. At -18°C (0°F) the same battery may start the
engine only three times. Low temperatures also increase the time necessary for
charging a battery. A battery which could be recharged in an hour at 25°C (77°F)
while flying may require 5 hours for charging when the temperature is-18°C (0°F).
CAUTION: WHEN THE AMBIENT TEMPERATURE IS BELOW 0°C (32°F), THE
ENGINE(S) SHOULD BE STARTED USING BATTERY POWER INSTEAD OF A
GROUND POWER UNIT. THIS PROCEDURE WARMS THE BATTERY AND
IMPROVES ITS CHARGE ACCEPTANCE. IF THE BATTERY IS NOT USED TO
START THE ENGINE(S) IN COLD TEMPERATURES, THE BATTERY MAY NOT
HAVE SUFFICIENT EMERGENCY POWER DURING FLIGHT.
NOTE: SOME RG
®
SERIES BATTERIES CONTAIN INTERNAL HEATERS THAT
ARE POWERED BY THE AIRCRAFT ELECTRICAL SYSTEM. ONCE THE
AIRCRAFT IS POWERED UP, THE HEATERS WARM THE BATTERY TO
IMPROVE ITS CHARGE ACCEPTANCE IN COLD WEATHER. IF THE MAIN
BATTERY CONTAINS A HEATER, IT IS NOT NECESSARY TO USE BATTERY
POWER TO START THE ENGINE(S) IF GROUND POWER UNIT IS AVAILABLE.
In Summary: During cold weather, keep batteries fully charged. Make every effort
to conserve battery power. Consider using a heated battery to improve charge
acceptance.
Table 3. Electrolyte Freezing Point versus Battery State of Charge
State of Charge (%)
Freezing Temperature
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