I work long hours on the road. I'd like to have a portable charging option because I am a heavy user and some days I'm away 18 hours from home. I don't like car chargers because I've had mixed results with them. Often I would feel my previous phone, Droid X overheating when using them. . Has anyone tried a battery pack/charger with their Razr Maxx HD? I'd like to be able to recharge on the fly and have the pack shut itself down at full charge..