I've had problems with Traxxas NiMh batteries before, I had one that smoked and melted some of the battery cause of a bad cell, and I had another one (same type of baterry, 3000mah 7 cell hump pack) that also had a bad cell. The second one didn't smoke though so that was good. Traxxas replaced...
Just my 2 cents but one thing I would recommend is either only running NiMhs in a car or only running LiPos in a car. It's easy to forget to switch your car from LiPo mode to NiMh mode and running it in the wrong mode is a really easy way to ruin your day lol. So if you forget things as easily...