My solution was not cheap- a permanent whole house generator with an automatic transfer switch. This allows my aquariums to continue running, as well as my private well pump, furnace, appliances, etc. I own my home, so this was my solution after a couple lengthy power outages in the last few years. It uses propane for the fuel source.
Eheim Pimpette #270
Eheim Pro II 2028; Classics Series -2215, 2217, 2260, 2262; Pro 2229 Wet/Dry