This instructable will show you how to make a long lasting ‘AA’ battery backpack for your Arduino. Why not use a 9V or lithium battery? Well, here’s why this maker chose to use AA’s instead:
I recently bought an Arduino Diecimila board. It’s awesome and the applications, you can use it for or with is almost unlimited. However there’s a problem when you want to use it in portable applications. You can use the Liquidware lithium backpack, which is a good way to power the Arduino. There’s a problem with the backpack though, cause when the battery dies, you’ll have to find an USB port or another external power source to charge it. You can’t just replace the battery. You can also choose to power your arduino with a 9V battery and the built-in regulator of the Arduino board. The problem with this setup is that 9V batteries doesn’t have a very high capacity, so they’ll die faster.
Learn how to make an Arduino AA Undershield
In the Maker Shed: Make: Arduino