The move to fully wireless Di2 on the new XTR M9200 groupset meant Shimano needed a fresh way to keep the rear derailleur battery topped up, and the EC-DN100 is the answer. This is the dedicated charger for the BT-DN320 battery that lives inside the wireless XTR Di2 rear derailleur — you pop the battery off the derailleur, snap it into the charger, and plug the whole thing into any USB-C power source. It's small enough that it disappears into a gear bag, which matters more than it sounds like it should when you're packing for a race weekend and trying to keep the cockpit clutter down.

The important thing to know up front is what this charger does and doesn't work with. The EC-DN100 is purpose-built for the BT-DN320 battery used in the wireless XTR Di2 mountain groupset. It does not charge the BT-DN300 battery found in semi-wireless road Di2 systems — Dura-Ace R9200, Ultegra R8100, and 105 R7100 all use a different setup where the EW-EC300 cable plugs directly into the rear derailleur. If you're running a mixed garage with both road Di2 and the new wireless MTB system, you'll need both chargers on the workbench.

USB-C on the input side is the practical win here. Any laptop, phone charger, portable power bank, or wall adapter you already own will run it, so there's no proprietary brick to lose or forget on a trip. That's a meaningful upgrade over the older Di2 chargers that used their own dedicated cables and made travel just a little more annoying than it needed to be. Toss the charger and a spare BT-DN320 in your travel kit and you've got redundancy for a full race season.