This sled is designed exclusively for the popular 1s 400 mAh battery only, and will not accommodate a 9V battery. In order to use this sled and battery you will need to swap or adapt the 9V connector for the 2.0mm JST socket included in your sled kit. It is the sole responsibility of the flier to ensure the correct connection polarity. To secure the battery, slip the battery into the pocket on the back of the sled with the wire end toward the top. Place the battery retaining clip in place with the wire passing out the top, and secure with two 4-40 screws from the front of the sled. Check to make sure the wire has not been accidentally pinched.