Hi,
He's right any stick pack (2cell) will fit but make sure you check the dimensions before buying, unless your prepared to modify your chassis.
Soemthing like this would be good:
http://www.smddirect.co.uk/79835-lrp...-30c-7-4v-3660
SMD sell a range a stick packs, LRP one are probs your best bet.
Steven