That's really the heart of the matter. A battery air pump is only going to get you so far. A generator is the best way to protect your tank over a longer shutdown. I think you can pick up a 1000watt unit for about a hundred bucks. Ocean state job lot occasionally has larger champion generators that sell for about the same price after a crazy deal rebate.That might be the case. I have one on my 180 but I have a battery backup that will run a circulation pump for 20 hours. If Power is out for more than a couple hours I have a genny that comes out.
Definitely agree that automatic battery air pump is a great first line of defense and a whole lot easier than dragging the generator out. My point is a short-term battery fix isn't going to keep your tank from going to 50° but with everything in life you pay your money and you take your chances.Most times there is a problem with a power outage it will a a short interuption. Probably when your not home or sleeping at 4am and only last a couple hours. O2 depletion will happen quickly (faster than fresh water) and a fish could die leading to a release of NH3 which could chain reaction. Auto start air pump and/or circulation pump battery back up is the better 1st line of defense.
I've used my genny once in 10 years.