Shimano E-Tube Di2 Internal Battery
If you want to ninja your Di2 setup, you'll need a Shimano E-Tube Di2 Internal Battery. You can hide it in most seatposts, for a clean, fast look. You will need to also pick up a 3 or 5 port front junction and internal battery charger so you can juice it up when you're running low, that way it can be charged without getting access to the battery. NOT
compatible with 7970 Di2 systems.