Shimano Dura-Ace 7970 Di2 Rear Wiring Kit for Medium Frames, 830mm

Shimano EW-7970 Di2 Rear Wiring Kits
All external wire kits include a large battery mount which is secured underneath a water bottle cage, typically on the downtube
Dura-Ace 7970 Di2 and Ultegra 6770 Di2 components and wires are not cross-compatible; the battery and its charger are universal