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King Air Battery Drain

September 2009

Certain model King Airs are subject to the battery being discharged below minimum starting limit if the aircraft has been static for even a few days. The cause of this might be the cockpit blowers.

The blowers are directly connected to the hot bus so they can operate after the battery switch is turned off. This occurs by design so the blower can operate if the electric heat has been in use and has not had time to cool before the battery switch is turned off. This causes a low but constant drain on the battery.


If the aircraft is going to remain static for a few days or more, the battery should be disconnected or monitored for discharge below minimum starting voltage. If the battery is below 23 volts, it should be charged. If the battery is below 20 volts, it should be removed and have a capacity test performed.

Please contact a Duncan Aviation King Air Tech Rep with questions about this or other avionics or accessory issues.