I bought a 1900mah "brick" that I can plug into the phone which then acts as a charger or I can use to talk off of. I charge it separately and just carry it in my briefcase or wherever. I got it mainly so that if I'm not near something to charge (I don't really think the car charger is something that I can use), I can plug this in, throw in in my briefcase, and attend my meetings or whatever. When I need it, it's probably all charged up.
I wish getting into the back was easier, otherwise I'd just have a separate battery. I bought into the Otter case and rubber bumper, so getting that on and off is no easy chore...not something I want to do once a day.
Kurt in S.A.