What Battery?????
You can get some Hecells at edogfight.com, and I believe Mountain Models has KAN packs and 720 AAA packs.
The KAN's perform better than the Hecells IMO, but they are also about 1 oz heavier. The 720's won't push as many amps, but they weigh about 1/3-1/2 less than the larger cells.
Most people use 7 or 8 cells, but if you're not worried about motor life, go with 8.
Jason