PERFECT FIT Flysky RC Plane Controller Battery Cover FS-i4, FS-i6, etc.

A remix of a perfect model makes it an even better fit, making sure that it can fit. All credit for the sleek aesthetic and 99% of the design goes to benbojangles: https://www.thingiverse.com/benbojangles/designs

There are two versions. Both should stay in place no matter how much shaking the controller will endure under any normal circumstances however, the tight fit will ensure a fit which you will not be able to dislodge with just your fingers and will feel much more comfortable and reliable during flight. The first time you put it in, you will hear a sna,p which is the rest of the support material coming off, which you will be able to remove with your fingers.

Happy flying!