Are you looking for something that automatically kicks on when the AC drops or a pump you activate when power drops?
If manually, I have used the Marina battery air pump. Have two of them and they work wonderfully. Real life savers when moving. The thing is, I have never found one that will work for a really deep tank. So you might need several and I also recommend not using the airstone because of back pressure. Just weight the line down. Here is a AC/DC unit that I have not used but might work: