Shimano Di2 BM-DN100-S Battery Mount

Somehow, Di2 cant help but keep getting smarter. With a new Bluetooth battery and Shimanos E-Tube Wireless app, you can now change your shifting preferences wirelessly in the middle of a ride with a smartphone or ANT+ head unit. If you have your drivetrain set up externally, youll need this mount, as well as a compatible wireless unit or display to go wireless.