Review on AQQA Aquarium Lithium Battery Air Pump - Multifunctional, Rechargeable, Energy-Saving, and Quiet Oxygen Pump with One/Dual Outlets, Air Stone, and 2600mAh Battery - Suitable for Indoors, Power Outages, and Fishing by Jessica Brown

I love that you can plug it in and out of your tank and if the power goes out it will automatically turn on and produce air. This is in a 55 gallon cichlid tank. As you can see from the photo, quite an impressive amount of air bubbles is obtained. Sitting for 10 seconds on a 10 second power off cycle is said to last over 24 hours, which is great for a backup like this. It's very quiet, you have to be careful when you take it out of the tank and be careful not to leave it on because you'll never hear it.