auxiliary power
electric power that is provided by an alternate source and that serves as backup for the primary power source
en-US/ɑɡˈzɪljəɹi ˈpaʊɚ/
en-GB/ɔːkˈsɪlɪəɹɪ ˈpaʊə/
electric power that is provided by an alternate source and that serves as backup for the primary power source