Do like i did a, although you might not want to spend this much.

I got two Zippy 5s 4000mah to use for heats and one PQ 5s 4350mah for longer finals.
The Zippys you get 16 - 17 mins no probs and the PQ 20 mins no prob .

I also went with these packs because i didn't want to go over 600 grams in my buggy.

Another note on the Zippys , even though they are 4000 mah i'm getting about 4300 mah in them after charging