from what I am understanding the power being applied to charge that phone in the vehicle charges at a higher rate than in-home chargers. It takes a much less timeframe and is to be monitored rather vigilantly. Yes it does heat up and yes it charges more rapidly, especially the lower the battery is what i have experienced. Also unlike the in-home charging, it is not to be left on a car charger as it will fry the battery.
I have read this in the Storm manual and also been told from the lads at VZ. That is good enough for me as first hand experience and feeling the heat then knowing why it is being created.

Tend the charge. Maintain the battery.
and as always.. good luck.