There is a Swedish company that is about to pruduce a hydrogen-powered fuelcell for recharging cellphones. It's not for sale until this fall though, so it'll only be for the next camping trip.

The charger including hydrogen container will be the size of a PDA, and contains 50Wh per gas tank (should be a couple of weeks use for the 770?). They're hopng you'll be able to buy the disposable gas-tanks at 7-11...

http://www.myfc.se/