Yes, but let's say it's the middle of winter, you have no power for 1 day and some how you can heat the room to a constant 80 degrees.
Can you cover that?
Let's assume you have the biggest UPS that APC makes, a 1500VA unit.
Let's keep my skimmer (70w) and my pump (65w) going for as long as we can....
1 hrs 47 mins
Not bad, would have covered half of the last power outage I had from the last big set of storms.
Let's move to the middle of winter and assume that I don't plug in the battery backup until I need to keep the water temp from dropping far enough to kill everything in my tank. (Sometimes I have to travel for work and can't heat water on the stove to float in the tank. This could be an issue as did happen this past winter from the ice storm we had, but fortunately I was home.)
70w + 65w + 250w
32 minutes
Wow, not good, considering how some areas this past winter were without power for about a day.
Lets go another route. You leave for work and go out to dinner with the guys and have a few beers, coming home, oh say, 16 hours later. You come to a 70 degree fish tank from a normal, constant, 81 like mine, no skimmer, no return pump, no heater, no circ pumps, no lights. Looks like the main breaker for the house tripped when the power company came to do work on the lines outside your house. Too bad for you. (Had it happen the week after I setup my fish tank.)
Let's say you have 960 watts (8amps) worth of equipment in the above sample. I can run that off of a random AGM battery online that I looked up (GPL-24T Lifeline Deep Cycle Marine Battery, the smallest one they have) and run it ALL for just over 8.5 hours. That's one battery. Add a second, get another 8.5 hours. Cut the load in half, like my HOB skimmer and SEIO pump with a 250watt heater, and you've got better than 17 hours per battery. (Smaller loads are more efficient on "deep cycle" batteries.)
This is what I'm trying to do. Find an affordable, reliable, easy to setup system. that can be scaled to work for anyone. All the parts I'm looking for are off the shelf, minimal work to hook up, and can be moved if I move or if someone needs to use it.
If someone has something that can power my fish tank with true sine wave output for more than 2 hours with an off the shelf solution, I'm all ears.