Granted, my 13.5 nano is small, but when I tested it during my install 2 weeks ago, it powered my 186GPH 8W Sicce return pump and a 50W heater for about 24 hours (tank has a lid, heater doesn't come on that often) with just a basic 1500VA/1000W UPS. If I don't run the heater, it'll last me about 36 hours.