Have you seen these? They're awesome! I'm tired of carrying a dozen AA batteries for my MP3 player, this is a great setup.
eTankbags powered by Powerlet provides a great solution to charge cell phones, music players, GPS or radar detectors. Use them to run bike-to-bike communications or power electric clothing. A great way to consolidate cables too. Simple to install. If you have an accessory outlet installed on your bike choose Kit A, if not choose Kit B. Kits include everything you need to power up your bag. Additional internal cables may be necessary to add more than two outlets or to add an additional kind of outlet.
I just put one of these units in my BMW tankbag and it works great. Don't know why I didn't think of this long ago?
I use it to charge my cell phone and PDA while riding and using GPS on my PDA. Will use it for electric clothing this winter.