I run these:
http://www.hobbyking.com/hobbyking/s...arehouse_.html
The wires come out the side and fit nicely between the motor and speedo (I run Deans connectors so as not to blow anything up!). They're punchy enough for my 5.5t, and easily last the 5 minutes. Compared to the other packs I've fit in there they're less than a quarter of the price and deliver equivalent performance. Can't recommend them enough for the Cat.