When building a bike for Di2, there are many ways of arranging the wiring. Some run the cables externally, and some run them internally. Several different ways of mounting the battery have also surfaced since the advent of Shimano’s electronic component group. Read on and check out these images to see how we at Zinn Cycles have achieved a very sleek and elegant system for Di2 with minimal compromise in the frame’s structural integrity. 
We have made a convenient entry point for each of the shifting cables so that your custom titanium Di2 bike will look very sleek and very little clutter of cables.
We make a small hole with one of Shimano’s grommets at the very end of the chainstay, so the rear derailleur cable goes right into the chainstay and looks very clean. It also keeps the chainstay stronger than if we were to drill the hole into the side of the tube.
The wire goes from the shifter and into a small hole in the down tube so the wire can be hidden all the way until it reaches the derailleurs.
Instead of drilling the large hole that shimano suggests in their guidelines in the side of the down tube, we put ours in the bottom of the bottom bracket, which has much less effect on the strength of the bike. Then the battery is mounted under the down tube hidden by the chainrings and is very inconsicuous. The chainring gets in the way a little when opening the battery pack, but it’s worth it for the clean look.
