MIL-PRF-8565K, MILITARY SPECIFICATION, BATTERY STORAGE, AIRCRAFT, GENERAL SPECIFICATION FOR (25 JUN 2001) [SUPERSEDING MIL-B-8865J)., This specification covers the general requirements for rechargeable aircraft storage batteries. The batteries are nominal 24-volt batteries that are generally used for medium current engine starting/utility applications, have non-removable covers, and designed for maintenance-free operation (see 6.15.10).