Your charger may be too small, mine charges faster on my car charger than with the ac charger.
Sent from my Thunderbolt!!
Does it have to be the stock tbolt charger or are all the htc car chargers 1 amp?
After doing a little bit of research, I bought the Motorola Micro-USB charger . I've used the step by step GPS navigation with the display on, and it will still charge the phone. The charger's max output is 950mA, and the TB's max input charge is 1A (1000mA). That's pretty darn good. It has nearly 600 reviews on Amazon with a 4.5 star rating, so you really can't go wrong with this one!