Round seatposts make ideal hiding spots for Di2 batteries, but the cylindrical battery needs something to keep it from rattling around inside the tube. PRO's Di2 Seatpost Battery Holder solves this with a two-piece resin sleeve that wraps around the battery and wedges securely against the inner wall of the seatpost. The flexible fin design compresses slightly to accommodate the minor diameter variations you'll find between different seatpost manufacturers, so it works with most round posts within its size range—not just PRO's own seatposts.

The holder works with both the BT-DN110 battery from 11-speed Di2 systems and the newer BT-DN300 used in 12-speed Dura-Ace, Ultegra, 105, and GRX Di2 setups. Both batteries share the same external dimensions, so the same holder fits either generation. You position the battery with the cable port facing down toward the bottom bracket, then slide the whole assembly into the seatpost until it seats firmly. The resin material provides some vibration damping, which is a nice secondary benefit for your electronics.

Shimano includes a stainless steel extraction tool with each holder because pulling the battery back out for service or bike packing can otherwise be frustrating. The tool hooks under the holder and gives you leverage to break the friction fit without damaging the battery or seatpost interior. It's the kind of detail that matters the first time you need to remove the battery for transport or troubleshooting.... Read More