I have run the hyperion packs and thought they were ok, a 3s 1800 with a Hyperion yc-22 motor in a rc18.....I prefered the Hyperion motor to the Mamba 6800 , My first choice would be a flightpower pack but it is 6mm too long I dont know if you could trim material to fit and if that doesnt work my 2nd choice is the Zippy good bang for the back

http://www3.towerhobbies.com/cgi-bin...?&I=LXRVY8&P=7


http://www.hobbycity.com/hobbycity/s...00mAh_2S1P_20C


the zippy is a little wide but can fit with a little dremel work