Battery bottle.

We love the sharp, corrective shifting of Shimano's Di2 groups, but all that tech goes to waste without a power source. Enter the SM-BTC1 Di2 Bottle Cage Battery Mount — or rather, insert a BTR-2 battery into this thing and let the shift levers fly. The SM-BTC1 mounts on your frame's water bottle cage bosses, where it serves as a Junction B in the Di2 system. It's got six E-Tube wiring ports, and it keeps things tidy with internal wire organization and routing.