Read all about 'em
This is hands down the slickest solution to a common problem I've seen in a bloody long time. With built in Lithium batteries in pretty much everything now (hell I can't believe my DS Lite has 'em) the practicality of batteries (even rechargable ones) has been fading for a long time. However, if said batteries could be recharged right off any USB port (lets face it, USB ports are awfully common near anything technical) and their practicality grows in leaps and bounds. I poked farther into their site and they have plans for a 9V battery variant and even a line of (GENIUS!) cellphone batteries that recharge off USB ports.