I'm running a Losi 8ight-e and we're running Turnigy 4500mah 4S for qualifiers that give us approx. 12 minutes on full bore. We run a converted Turnigy 5800mah 4S (2 x 2S soldered together) for the finals which give us a maximum of about 16 minutes on full bore.
Hope this helps.
Ps. These were all bought from
www.hobbyking.com