Mine came with a 700 mAh pack. I now use an 1100 mAh pack that I bought from a fellow at a swap meet. He has a small business making and selling packs and other RC accessories. Sometimes the 700 pack would run down during a long day at the field, especially with two planes. I'll try to find his card.

You can use packs from different sources, as long as you're sure it's 9.6 volts and the right shape. I have bought the Tower Hobbies brand packs and soldered on a Futaba connector. Or the safest way is to buy a genuine Futaba brand pack.