I use a Team Helotes 2600mah battery pack on my 8.5 but if you are using the 8 you would need the updated box.
or you could get this battery:
http://www3.towerhobbies.com/cgi-bin...&I=LXMEY1&P=ML
and this charger
http://www3.towerhobbies.com/cgi-bin...?&I=LXHCF1&P=M