you can get cheap 6 volt packs on e-bay, they cme with the proper plug, hump packs will fit in the same place, you will see more actual voltage and runtime from a six volt pack than 4 aa's, also, plugging the battery into an open third channel rather than the battery slot will give you servos more voltage
http://cgi.ebay.com/2-RC-6V-NiMH-140...QQcmdZViewItem
a link