I'm running 1500s 7.2Volt 6cells. It's pretty much stock with the twin 540 motors, but I upgraded to an ESC. I would like to increase my run time per battery from 10 minutes, which is about what I'm gettin with the 1500s.
Yes, nearly any stick pack configuration will fit in the double B. You can also get away with running the real cheap generic e-bay type batts in the truck and they are usually sold by the pair and are a lot cheaper than name brand cells.
check cheapbatterypacks, or onlybatterypacks . coms out. they make custom packs, im not familar with that truck, but i had em make me a 8 cell for my blitzer beetle that fit the factory spot !! and go with 4200's !!