Battery powered Aquarium Air Pumps are common and can be easily bought from Local Fish Stores. But the downside to such pumps are that you need to replace the batteries each time they run out, or recharge the batteries with a separate charger. You also need to be there to switch it on in case of a power loss in your house.
In this instructable I will show you how to modify such an air pump to recharge and start up automatically in case of a power loss.
List of Necessary Parts:

- LM2596 Buck (Step-Down) Converter - 1
- 5V Relay - 1
- TP4056 Charging Module with DW-01 Protector - 1
- Copper Dot Board - 1
- 18650 Rechargeable Battery (Li-Ion) - 1
- Terminal Connectors (Optional) - 2
- PCB Spacers (Optional) - 2
- Double-Sided Tape - 1
- Copper Wires
- Diodes (1N4007) – 3
- Micro USB Cable - 1
- USB Charger - 1

Battery Powered Air Pump (the main ingredient - doesnt matter which brand or company, as long as it works) - 1
These parts are readily available online and can be found in local electronics stores as well. I would like to give you links to these parts but I myself bought these locally so I would not want to recommend you sellers which I do not have any experience with.”

Link