You could just get some rechargeable AA/AAA's and a charger, but if you want the usb, pony up just a little ($5) more and get the Cygolite Hotshot 2W for the seatpost/rack. Check out this thread in Electronics: http://www.bikeforums.net/showthread...able-taillight. And you might want to spend some time reading this little bit on night time visibility that was created by a BF member- http://www.mechbgon.com/visibility/index.html