Maybe you want to take your design and project mobile, for instance, up in the mountains away from your vehicle and any plug in outlets. It might be useful to have a battery powered device whose batteries you never change, but just crank up once a week. Or better yet, maybe you want to take your Arduino to the coffee shop and not have to look for an outlet or USB connection. Well, here's a quick little way to power your development board from a battery that never (well, you know) runs out.
I've taken a hand-crank-powered flashlight and hax0red it to power my AVR and Arduino development boards. The battery lasts for a good long time and if you crank it a few times before you use it you'll find you'll get a solid 3.5V out of it (depending on your battery). Plenty enough to power an AVR ATtiny, ATmega, and ATxmega, as well as other 3.3V devices like the STM32F ARM MCU indefinitely!