This might have been covered some time before, heck this might be an idea done so many times its boring, but with about building a snap, clip on cover for a cell phone that uses solar power to recharge it, you made a kinetic charger that was cool, but if you were deserted on a desert isle, it would be far more likely solar powered case would be around than a bulky charger. Since some solar panels can even charge well in incondesent lighting it might prover to be a useful build.