ou obviously need a 4 or 5 AA battery pack. What size depends on what flying time you expect and maybe what plane it will be used in. If you just want to get in 6 flights with a 5 lb. plane then a 600 mah pack will do. If you want to fly a 8-10 lb. plane or fly all day then around a 1500 mah battery pack would be better. Just to note, batterys are getting better and cheaper all the time so you may have less trouble finding a 1400 mah pack or larger than what used to be the standard 600mah pack. One word of caution, make sure that you get a charger that is rated for the battery pack. For a 1500 mah pack you need a charger that will supply 150 ma. power for overnight charging. You can use a wall charger rated at 60 ma output but you won't be able to fully charge overnight! [8D]