Shimano BM-DN100 Battery Mount for SM-BTR1 Di2 Battery-Pack - black - 2nd Choice

2nd Choice. Further information in the product description.

Shimano Dura-Ace 7970 Rear Wire Kit - Components

Shimano EW-JC130 Y-Split Rooting Electric Wire for Di2

Shimano Ultegra and Dura-Ace Di2 Electronic Shifting – Everything

SHIMANO XTR DI2 Battery Case

Shimano Ultegra and Dura-Ace Di2 Electronic Shifting – Everything

Shimano Di2 Battery Mount BM-DN100 - bike-components

BM-DN100-S, Battery Mount for EW-SD50, Short, for External

In-depth guide on upgrading your old Di2 bike

Hands On Bike: Bike Friday HaD: Di2 Battery Placement and Wiring

Hands On Bike: Bike Friday HaD: Di2 Battery Placement and Wiring

BM-DN100-S, Battery Mount for EW-SD50, Short, for External