I agree about the voltage...keep it under ~5.2V but better yet, why not jigger up what amounts to an external surface mount panel that uses a USB splitter cable or even a direct connect then sent the current straight through the existing power system. You get proven charge regulation as well as likely can rig it so you don't void any warranty.
Still I love the idea however ya make it work...but remember, if we don't see pics then it never actually happened.
