This is interesting (albeit expensive and relatively new technology):

Summary: The HydroPak claims to replace batteries and generators with replaceable cartridges that can sit on the shelf indefinitely, and can later be activated with water for about 12 hours of power. Silent operation and no emissions so they could run indoors. Each $20 dry cartridge cranks out about 400 Watts through an AC outlet and two USB ports. Of course, for this pioneering technology you would have to pay $400.

Here is a copy of the press release from the company (in .pdf):
HydroPak Press Release

Millennium Cell Homepage:
Millennium Cell