battery-backed

Short definition from Wiktionary

Adjective

1. 1
   Of a device, using a battery to maintain operation when not powered by the main electrical supply (e.g. during a blackout).
2. 2
   Using a battery to maintain volatile memory when powered off.
3. 3
   Of saved game data, written to a volatile memory chip in a video game cartridge to maintain the data when not in use.