Report as inappropriate

Hollo. You can use 9Volts batteries like this: http://upload.wikimedia.org/wikipedia/commons/thumb/8/8d/Duracell_9_Volt_0849.jpg/200px-Duracell_9_Volt_0849.jpghttp://upload.wikimedia.org/wi...

With those it has been tested and works. You have the exact space to place them on the bottom, below the chassis.

I myself use a LiPo battery with 2 cells ans 1.2 AH. And I place it under the Arduino board.