I am just about to write in another thread about my battery improvements tonight on the 4.0.4 IMM76 release. It is much better, a lot better than I am used to, even over IMM26. I was about 50-60% battery life remaining after about 8-9 hours. I have 60% after 13 hours right now. So I'd say you have something going on, I have Wi-Fi on all day, and I set it to not remind me of open networks as I use my company's Wi-Fi, and I use GPS. I have a lot of refresh services about 1-2 hours for the ones I care about, other less important about 6 hour refresh periods. I use latitude and google talk for some comparison, as I know some who don't. Sorry you're seeing these issues, but I am not experiencing the same and thought I'd at least let you know if you suspected a phone issue or a battery issue.
As far as the car charger issue, I'd see what the output is rated at, the adapter that is. I got one at microcenter that outputs 2 Amps instead of the .5 amps that you typically find around and I am able to charge while using navigation or Waze and Slacker at the same time. I also blow a vent of cool air at it as I know it can get very hot, and if it gets too hot, it won't charge as the over temp sensors will prevent it from charging.