a 1500 mah 20c pack would be plenty, 1000mah 15c would prob be fine depending on how many you were running.
but honestly i would buy life battery packs not lipo's, their safer (no explosions/fires), can recharge faster, and dont cost that much different
http://hobbycity.com/hobbyking/store...8&ParentCat=85
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=MCD
or at all-battery.com under their airplane batteries (their site isnt working for me some for some reason.)
or you could make your own pack for like 10-20 bucks useing all-batt life round batteries