Built-in battery for Shimano Di2 groupsets.

Specifications
Compatible charger: SM-BCR2
E-Tube Port
Type: Built-in battery
Battery: Li-Ion
Rated Voltage (V): 7.4
Rated Capacity (Ah): 0.5
Rated Capacity (Wh): 3.7
Compatible Charger: SM-BCR2
Average Weight: 50g

Mfr Claimed Weight
50g