I have modified a way to run headlight/taillight off of a cell phone.
I have also found a 6V system that can be made for right around $25.00 here's the thread....
HT 6v Charging System w/- ground - MotoredBikes.com: Motorized Bicycle Forum
I am currently trying to hook up a couple of LED flashlight heads to my cell phone.
If you have any more questions just let us know that's what we are here for.