Before you purchase any batteries I would talk to some guys out at the track about your specific "spec" rules. General rule of thumb is 6 cell NIMH (7.2v) or 2S (7.4) Lipo.

Once you figure that out go with a reputable company for your batteries. Spend a little more and get something that will last. Do your homework as well. Lipo and NIMH charge and discharge differently. With lipo you can also ruin a battery pack by over-discharging it.