Most GTB guys run a hobbyking battery, even if your not a fan of buying from them, its the best softcase battery that fits in the car. Some of the team drivers use it.
I think its this one, but its been a couple of years since i had to buy one, so double check the dimensions.
http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html
If your looking for a hard case, then your options are the vampire pack, or shumacher do a hard case intellect pack. It looks neater in the car. I know a couple of the team drivers tried it, but i cant remember what the conclusion was.
__________________
Tom
TLR 22-4 2.0, TLR 22 5.0 AC Elite,
Kindly Supported by Trackside Spares, TLR, Spektrum and Horizon Hobby