Tucking the battery inside the rear derailleur itself eliminates the frame-mounted battery, junction boxes, and internal routing that defined previous Di2 systems. The BT-DN320 slides into a protected cavity within Shimano's wireless rear derailleurs, where it powers the shifting motor while staying shielded from rock strikes, mud, and trail debris. This is the battery that makes Shimano's fully wireless mountain and gravel drivetrains possible—without it, the derailleur is just an expensive paperweight.

The battery works with all of Shimano's current wireless Di2 rear derailleurs: XTR RD-M9250, Deore XT RD-M8250, Deore RD-M6250, and the gravel-focused GRX RD-RX827. If you're running any of these derailleurs, the BT-DN320 is the only compatible power source. The derailleur itself doesn't ship with a battery included, so you'll need to purchase one separately when building a system from individual components. Having a spare on hand makes sense if you're traveling to races or doing multi-day trips where charging access might be limited.

Capacity sits at 305 mAh, which Shimano rates for approximately 750-1000 kilometers of riding depending on shifting frequency and conditions. Real-world range varies—heavy shifting on technical terrain burns through charge faster than smooth gravel roads. The battery charges via the EC-DN100 charger (sold separately), which uses USB-C power and takes roughly 90 minutes for a full charge. Removal for charging requires no tools: slide the derailleur's battery cover off, pull the battery out, and pop it into the charger. You can check charge status through the E-TUBE PROJECT app or by pressing the button on the derailleur body, which triggers LED indicators.... Read More