Arduino board requires a USB cable connected to a laptop/PC or an external AC/DC adaptor for power supply. If you want a portable Arduino-based project, you need a battery for power supply. 9V PP3 is ...

Beyond that, the rest of the build is comprised of pieces from an old 9v battery. Once you have it all put together and tested, you can clip in a 9V battery and switch it on and off easily.

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.

Makers and hobbyists looking for a more substantial portable battery pack that they can make themselves, should check out this excellent DIY power bank created by Instructables user “tobychui ...

Options to power the Arduino Nano include USB, VIN, and 5 volt pin, meaning you have power options for almost any situation.