Vortechs and their battery backup works well for smaller tanks. Can run the pump/s for up to two days. For larger tanks you can chain Vortech backups together or replace the Vortech backup and save money with bigger deep cycle batteries (search RC for how to do it). There are other pumps that do the same as Vortechs but I have no personal experience with them.
Of course batteries are only really good for water circulation, no lights, heater, or anything like that. For power outages longer than a couple of days a generator is necessary.