Meet the Minty Boost. It’s a $20,- DIY kit to build a dual AA battery USB charger to give your iPod or other USB charged gadget an extra boost. In this example it’s built in a candy box, but you can obviously build it in anywhere you like (in a back pack or jacket?). Inside a USB cable are two smaller cables that transport power. Gadgets that charge over a USB connection like the iPod don’t actually need to be connected to a computer to get charged but only need those two little wires to transport 5V of power.

If you want to build a USB charger and really want to start from scratch you can also follow this guide from YouTube about building an iPod charger for less that $4,-. This guide uses an actual power adapter but if you manage to convert it to the correct voltage you should be able to replace it with batteries.