Never looked that close at that truck... that is some wonky suspension! Surprised traxxas didn't sue them for having cantilever shock system on it!
Looking at it, the size of the battery boxes is very limited like the e-revo, so you would need to measure the box and then figure out what would fit. Odds are, it's intended to run on 2 2S packs or 2 3S packs, but I'm guessing if he has an 80A system on there, he will likely be limited to 2 2S packs.
SMC makes some fairly standard sized hard case 2S packs I used to run in my ERBEv1, 7200mah 2S:
The most cells you can run according to the specs are a 4S LiPo. This is 14.8v. For bashing, you could go with a 5000 mAH 4s battery. Just be sure that the battery fits in the holder on the vehicle.