Original Physics Theory: Charging an iPod with an Onion

Imagine the Earth has been turned back to a dark prehistoric age. The power grid is down worldwide, streets are deathly quiet except for the occasional packs of wild rusted cars stranded on the roadsides. In the pitch black night, you can barely see the flickering campfires in the distance. Like the other few survivors, you scavenge through debris to stay alive. And then one day, things get worse: your iPod -- which has been playing a two-hour DJ mix -- runs out of batteries! You are stunned.