This happened to my phone many times when using GPS over a long distance.
The alert would pop up saying that charging was stopped due to high temperature. And indeed the phone felt hot! Keeping it plugged into my car did nothing as it cut off the charge which is scary if you think about the battery venting on your dash.
I can continue driving using GPS without being plugged in but it wont last more than an hour or so and drains quicker than normal. The phone was pretty decent otherwise so I thought it was the battery and had planned to get a new one anyway.
When I went into the verizon office they said they'd replace my phone. I said no, i think its the battery but they said we'll try the phone first. Maybe they know of an issue?
SOo they shipped out a new phone (no new batt or card) and we'll see. I dont have any 3 hour driving trips planned to test it for awhile though.