lipo batteries

hey every i just picked up a Sidewinder ESC & CMS5700 combo for 60 bucks and a 49 min drive im putting in my xx4 i was wondering what would be a good size lipo batt.
i plan on racing this truck at my local track (oc/rc).

does anyone use this charger?? looks like a good charger and great price
and charges 6 cell for a brushless mammoth im working on =]

http://www.hobbypartz.com/thac6smbachw.html