The below stem wart is the 11 speed junction box / charging port / config button.
11 speed Di2 - Bluetooth wireless is an add-on option. It permits software updates and displaying gear selection on a bike computer.
Brifters/battery/junction box/derailleurs/(optional D-Fly Bluetooth) all hard wired.
12 speed Di2 - The Bluetooth is built in. Plus the brifters do not require being wired to the battery/derailleurs.
battery/derailleurs are hard wired.
Brifters, hard wired is an option. If used wireless, be sure to keep spare coin cell replacements.
The 11 speed stem junction box had no wireless function and no longer exists for 12 speed.
It was also available as a bar end device and a frame mounted device.
Barry
BTW - The above does not take into account the new 105 12sp Di2.
It’s brand new and may offer different functionality.
Last edited by Barry2; 07-01-22 at 08:14 AM.