(or any liquid, for that matter)
http://www.candlepowerforums.com/vb/showthread.php?332049-NoPoPo-Eco-Water-Powered-Flashlight-Set
http://www.japantrendshop.com/nopopo-eco-waterpowered-flashlight-set-p-539.html
yeesh, the very idea of a "hydro-electric battery", neat-o! But probably not usable large-scale in automobiles, imagine if you brake suddenly but the liquid sloshes around so much your car lurches around and you either induce nausea or the damn thing flips over...
Only forty five dollars!
The idea of hydro-electric batteries is neat. I guess there's a little water-powered dynamo in there? 300mA isn't a large amount of charge, though, compared to the 2,000+mA found in modern NiMH batteries. And it can only handle five charges, apparently. I'm willing to bet you only get an hour out of it before needing a charge.