This genuine Shimano small part is exactly the same magnetic charging port cover as came on your Di2 R9250 Rear Derailleur. The piece is designed to be replaced, because if you tore off a non-replaceable item and couldn't replace it, you'd be less than pleased. The cover keeps the magnetic interface from gunking up, and while water infiltration should never be an issue with an exposed port, the cover offers some assistance. Remember, this interface is your charging point, and the rear derailleur houses your important Di2 electronics. Keep your port covered.