What Our Gearhead(R) Experts Are Saying: "I just started running the BT-DN300 in my new Di2 setup, and the clean look is a major win. It fits perfectly inside the seatpost, and the extra SD300 port gives me the wired backup I want for longer endurance rides."When we want our Di2 system to be sleek, reliable, and ready for the road ahead, we install the Shimano BT-DN300. Designed to mount internally inside a seatpost or frame, this compact battery delivers steady power to front and rear derailleurs with a minimalist footprint. With three SD300 ports and full compatibility with Shimano's latest R9250 and R8150 12-speed Di2 groupsets, it supports both semi-wireless and fully wired configurations. For riders seeking extra reliability on long rides or remote adventures, that third port offers a trusted wired connection option-all without changing fit or form.