I use USB rechargeable air pumps for my tanks (up to 125 gallons) to get through hurricanes in Florida.
Here's an example.
The brands change from time to time, but the ones I use (which look similar to the one in the link) have:
- Adjustable output
- Constant running option
- Intermittent running option (10 sec on, 10 sec off, repeat)
- Off when power is supplied, on when power cuts off (this sounds important for you)
Mine are also waterproof (but not submersible). Battery lasts 24 hours running constantly. Because it's hot in hurricane season, I don't plan to run any lights anyway. My worst outcome was I lost 1 frogspawn coral after 8 days of just aeration, no light or air conditioning. All other corals and fish survived in my 8 tanks.
For the price, they're just great to have. I use them for my bait when I go fishing too. No more D batteries for me! And since they recharge off USB, those battery backups for your phone will charge them too.