The Shimano Di2 SM-BTR1 External Battery is designed to work with Shimano Di2 drivetrains. It is compatible with Dura-Ace 9070, Dura-Ace 7970, Ultegra 6870, Ultegra 6770, and Alfine Di2 systems.
Used, in good working condition. Needs to be recharged every 800-900 miles.