You can also go the 9v battery route plugged into the on-board regulator of the Arduino but the low mAh rating of a 9v won’t allow your project to stay running for very long.

Using an Arduino Nano board together with a 2.2 inch UART HMI display the batteries can provide up to 60w of power output.

The system operates off mains power but swaps to a 1000mAH 9V backup battery during a power outage, logging the time and sending out the SMS alerts.