I have a tanginykian tank with a lot of wild Frontosa in it so for the same reason I set up a home made UPS.

Battery deep cycle
Battery charger, make sure you get one that can go into float mode
Inverter

Plug the charger to the power, connect to the battery and connect the inverter to the battery. I only run an air driven filter off this but it runs 100 % of the time. If the power goes off the air pump keeps running for up to 36 hours.

Don't make the mistake of running everything off a dedicated or home made ups as you will just flatten it real quick.

This has saved me a few times and cost about the value of two of the fish.