Di2 custom; Shimano’s top of the line groupset made better since it’s difficult to mount the external battery neatly….
Modifying the Di2 to locate the battery inside the seatpost makes for a much cleaner setup. Electronic shifting and no clunky external battery.
The frame design has the cable access and clearance to make it all work, and my customer was pretty handy since he’s an electrician in the automotive industry and has sorted the seatpost mod. The batteries themselves weigh surprisingly little. Paul has made several more sets available, which require modification of the standard wiring harness.