Not sure if I'm remembering correctly from the keynote but, I think they mentioned the phone would have to be plugged into a USB port in the car ... Which would most likely mean it would be charging... Battery life might not be an issue at that point.
This is what I have been reading also.
I like the idea of seeing how much battery life is being sucked up by an app. I have a pretty good idea on what is killing my phone, but it would be nice validate what I am seeing.