[TrevorJ]

Hmm, that's actually pretty doable if coupled with pedal power (you'd either charge directly with a dynamo in this case or pump water to a higher elevation to store as potential energy). Back of the envelope math says you could do it quite easily in 15 minutes which isn't bad at all especially given the fact that you can't shove power into the battery anywhere near that fast.

Granted, this works much better with something like a light because LED's use so little power to run.

[jimrandomh]

Pedal-powered generators already exist. Using one to charge a battery is better than this gravity-energy-storage gimmick in every imaginable respect, but they still are not used much, because electricity is not scarce. (If you can afford to buy a gimmicky generator, you can afford to buy a real one instead and the real ones are cheaper and better.)

[TrevorJ]

That's pretty fair.