Abstract: A modular aircraft emergency backup battery system and methods for operating the system as well as removing and replacing the modules within the system are described. The system includes a module cabinet enclosure that positions and interconnects the modules. A wiring harness provides the necessary electrical connections to and from the aircraft avionics to recharge the batteries within the system to allow the system to provide a source of power when battery backup is required. The cabinet enclosure provides positioned connections for one or more battery cell modules and one or more power control circuitry modules. A hinged front panel allows access to the battery cell modules and provides a switch and an indicator for operation of a test circuit. The modular enclosure is positioned in place of existing aircraft emergency battery backup systems and connects to the aircraft within the same space.