This is a Battery Saver for the DJI Mini 2. It has been found that if you leave your batteries in the charging brick or Drone they do not self discharge as they should. This little thing clips onto the battery charging brick and allows you to keep your batteries in the brick but not connected, Thus saving space in the bag.

There is a video here that explains the issue with the Battery

https://www.youtube.com/watch?v=KLrhcwI1s68&t=147s