Shimano BT-DN300 Built-In Type Di2 Battery, SD300 Type for DURA-ACE/ULTEGRA
The third port is for riders who seek the redundancy of Shimano's 12-speed Di2 wired option. Shimano EW-EC300 Charging Cable - For Dura-Ace/Ultegra 12-Speed Di2 Systems. Shimano Di2 Battery, BT-DN110-A-8, Built-In Type, W/Recycle Mark.