Shimano Di2 BM-DN100 Bluetooth Battery Mount for SM-BTR1

Comes with removable aftermarket mounting tab, may or may not be useful for your setup. Older Di2 setups running the SM-BTR1 external battery can gain wireless E-Tube connectivity and Synchronized Shift functionality without replacing the whole system, and this is the piece that makes that upgrade happen. The Shimano BM-DN100 Short Battery Mount isn't just a bracket—it's the master unit that adds Bluetooth communication to a Di2 drivetrain that predates the wireless era. The short version is the one to grab when the downtube real estate is tight or a longer mount would crowd the bottle cage or bottom bracket junction.