The Brunton Torpedo charger is a light-saberoid* cigarette-lighter USB charger with an integrated battery. Use it to charge up to two devices in your car, then take it with when you go and it supplies 2800mHa of power (enough for two phone recharges) on its own. Sounds like a great travel-bag item, perfect for rental cars: charge your phone while you navigate with it in a strange town, then pocket the charger and use it to recharge halfway through the day.
*Light-saberesque? In any event, as close to a light-saber as is feasible without getting a license, so call it, perhaps, a "laser fencing foil handle" if you'd like. It is, anyway, sufficiently laser-foil-ish to satisfy any off-brand fantasies you have about being a Jad-eye warrior.