Technology : Lithium-Manganese Dioxide. Voltage : 3V. Minimum capacity : 125mAh. Dimensions : 3,2mm (H) - 16mm (Ø). Fits: Shimano Di2 12 Speed Levers. Sold as single battery.
Best Price: £3.49 from Merlin Cycles
Renata Lithium CR1632 Battery For Shimano Di2 12 Speed Levers – Silver / CR1632 Reviews