"With the same size as its predecessor, the slim BT-DN300 battery can be housed inside seat posts or frames ensuring a clean aesthetic. Now with 3 ports, the BT-DN300 simplifies wiring to front and rear derailleurs, supplying stable power at all times. The third port is for riders who seek the redundancy of Shimano's 12-speed Di2 wired option.
 
Compatible with thinner next generation electric wire SD300 and systems after R9250/R8150 series: RD-R9250, RD-R8150, RD-R7150, RD-RX825
Average weight: 52 g"
 
- Shimano