Are you using a car charger to do this or are you actually plugging it into a wall outlet (if you stop at night)? Using the nook cable is the right thing to do if you are using a car charger, but you need to use a car charger that puts out the correct current. There are chargers that put out about 2.1 amps to charge things like tablets. These are different than the standard car chargers for phones that only put out less than about an amp. I believe the standard (lower current) chargers will charge the NT, but it will take longer to do it.