Nothing! Everything you need to get flying is included in the box, including the "AA" batteries for the transmitter.
Advancing from a beginner heli to an intermediate flybarless heli has never been more seamless than with the 200 SR X. The Blade® 200 SR X is the first fixed pitch heli to employ SAFE™ technology for an unparalleled flybarless heli experience. SAFE technology helps to facilitate the learning process with beginner, intermediate and experienced flight mode options. Each flight mode utilizes varying amounts of bank limiting and advanced stability characteristics to assist pilots. Additionally, SAFE technology enables a panic button that can automatically return the 200 SR X to steady flight with the push of a button. This durable heli arrangement is complimented by brushless main and tail motors that make the most of the included 800mAh 3S 30C LiPo flight battery and 3-Cell LiPo AC Powered balancing charger. Best of all, with the ready-to-fly package you get a Spektrum™ DSMX® 2.4GHz transmitter and everything you need to get flying in little to no time.