^ I'd be more worried about this. My charger in my car actually charges my battery................
This is dependent on the charger you use.
Some cigarette lighter chargers put out proper mah ratings, others don't.
My old charger used to have issues... it would charge to a max of about 70% on the Triumph, and would only maintain a charge when using it.
The one I got to replace it will not only charge to 100%, it will also charge while in use.
I cracked open the old one to see what was inside and it was a butchering of resistors that were too large. This was probably due to being made for older phones that only need a low rating, like 200-300mah. These new phones run much higher, in the area of 850mah.
Using the Battery Stats app you can actually see the mah the phone uses when on, and it can easily use 200-300 for normal use, more if you are using it as a GPS or other activities.
So, TL;DR moral of the story - Get a current/new car charger, or just get a small inverter and use a wall charger in your car (many new inverters also include USB ports for charging).