Shimano Di2 BT-DN110-A Internal Battery
The power house of Shimano Di2 is a long-life Shimano BT-DN110 Di2 Internal Mount Battery that is both compact and reliable, taking shifting effort away from you.
Excellent sealing and reliability have been proven through repeated field tests in various riding conditions, including extreme temperatures, rain, mud, and cobblestone roads.
Using a hard wired battery system, this is both lightweight and accurate compared to current wireless technology (as a wireless system would require 4 batteries: one for the rear derailleur, one for the front derailleur, and one for each shift lever).
If mounted in your seatpost, we recommend you purchase the SM-BCR2 external charger so you don't need to remove your battery and seatpost every time you charge it.