I've had the same experience. I use Battery Monitor (puts the percentage in notification bar, and puts temperature/voltage/battery health in the notification window) and it's reported around 48 degrees Celsius and overheat in the battery health, and then it stops charging. This is when using Pandora and Navigation, also in a hot car. I was thinking it was my car charger at first, but I don't believe this is the case, as I'm on my second car charger and experiencing the same problem. I've also had the issue with two different batteries; the original battery, as well as the 1500 OEM.
After unplugging my phone from the car at 80%, my phone only lasted for about 10 hours (not normal), but I believe this was due to poor reception in the area I was in. I hope it's not due to the battery overheat earlier in the day...