Handful of Concepts - Hand Charger.

"Hand charged phone batter."

Seeing as I'm a festival enthusiast, is always becomes a real concern about phone battery, although there are ways of sustaining enough battery over the weekend - soon or later those chargers will run out. You could also pay to get your phone charged up but I mean come one, who wants to pay? Much like the self winding torches which requires hand power to generate enough battery life to produce a beam of light, there could also be something similar for a self winding phone charger. Just plug it in, wind it up and let your battery continuously charge, without having to worry about it running out.