With the 2250, you'll want to run a 4S setup. Aim for at least 4000mAh and a high enough C rating to give at least 150 Amps continuous, though more is always better. Do you want a hardcase or a softcase?

Check these out:
http://www.hobbyking.com/hobbyking/s...dProduct=10869

http://www.hobbyking.com/hobbyking/s...dProduct=10303

http://www.hobbyking.com/hobbyking/s...dProduct=10307

You should also check out the Gens Ace series. Much better packs for about the same price once you figure in shipping.

http://www.hobbypartz.com/98p-40c-50...-hardcase.html