The Di2 SM-BMR2 Battery Mount secures the SM-BTR2 battery to your frame. It's available in two lengths, Long and Short.
The Long version is installed to the seat tube or down tube via a single water bottle boss. The Long mount is available in internal or external variations depending on which cable routing your bike uses.
The Short version is designed for Di2-specific frames that have a battery mount separate from the water bottle bosses. The Short mount can be used with either internal or external routed cables. The Di2 SM-BTR2 Battery and electronic wire ares sold separately.
Note: This product is also back-compatible with Ultegra 6770 Di2 but requires component firmware updates. You will need the SM-PCE1 PC Tool to install these updates, which can be downloaded at http://e-tubeproject.shimano.com. Alternatively, the most recent firmware can be installed at your local Shimano Service Center.