Shimano's "A junctions" such as the EWRS910 are used to connect E-tube cables coming from Di2 shifters to the down tube E-tube wiring. Shimano's Di2 electrical drivetrain system eliminates poor shifting caused by dirt, corrosion and stretching while providing effortless, reliable, shifting.
For either specific frame mount or handlebar end plug mount
Battery level indicator feature
Additional charging point when using internal battery
Gear index setup switch to allow fine tuning via shifter buttons