If you can't get a battery backup, I'd get a D-battery operated air pump, put an air stone on it and drop it in the tank. That'll keep the oxygen in the water and I've used just an air stone for quite a few hours when the weather is warm. I do have an inverter that I use for power outages but you'd need to clip it on to a car battery. In the past I've used the trolling motor batteries from my boat during long outages.