LP-E6 Battery Plate

Everyone playing with small computers like Arduino's knows you need a 5V power input for your device to work. Using a higher voltage meens you need a voltage regulator, like a 7805 or something, but that gives heat and consumes power by itself.

Using 7.2V is the best you can do, because 7.2 volts in combination with a voltage regulator like the 7805 leaves you 5V exactly, with a minimum of heat generation.

The Canon LP-E6 is worlds most sold battery and is extremely cheap to buy, if you buy a non branded version. This is a 7.2 volt battery, so now you only need a battery plate, like this one.