I always struggle with the printed battery retainer. It really is a pain to get clipped into place…especially when the wires get in the way. So after some thought I realized that Velcro cord straps commonly used on laptop power cables would work really well to hold the batteries in. You can put them either on top and bottom of the battery box or on the sides depending on which way your battery goes into the box. In the pictures my batteries have wires that come out the sides so having the Velcro on the top and bottom makes it easy to put the battery in and take it out. The Velcro also stays in the plane so you don’t have to worry about misplacing the retainer piece. Pictured is the Spitfire MK XVI.