@Richard: Woah, this post is from a while back. I hope you found your answer in a timely manner. Man, there really should be more info on this in the wiki.
So yeah, the ESC's that ship with the hexa-b kit i believe support either 3 or 4 cell Lipo's. With 6x 880kv motors you definitely wanna be rocking a 4S Lipo's at around 5000mah. That should give you 12+mins of flight time under normal load, plus makes a great setup for adding another 5000mAh 4S in parallel to increase your flight time to around 22+mins.
One minor drawback with running 4S Lipo's is simply that many FPV camera and transmitter systems seem to take 7-12vdc, meaning you could safely power these off a 3S Lipo. When using a 4S Lipo it's necessary to add a voltage regulator. Switching regulators are more efficient but can then be a source of RF interference that can reek havoc with your video transmission. To help mitigate we simply add ferrite core beads or snap on rings that can be added to the output line of the regulator or even better an LC filter.
Hi and thanks for the reply. I got myself a 5500 3S which I guess is OK for flying w/o payload and general testing out. When I start hanging cams underneath I guess I'll get something bigger.
As you said, a proper wiki entry wouldnt hurt...