For the sake of this question, assume that you have a Di2 battery (e-Tube) SM-BTR2.
Also assume that you want to charge it without connecting it to the Di2 system on the bike.
Can this be done?
Is it a matter of just connecting 5v DC to it?
The etube wire is the only thing that can connect to it. I was hoping to be able to charge it without getting the 5-port front junction, but you can’t do it. You need at least one etube wire, the 5-port junction, internal charger and then you can charge it externally if you want.
You can charge it with the 3 port junction as well.
Confirming … you can charge it with the 3-port, too.
I had to look this up because I know I can’t charge with my three port box. It seems you can with the new 3 port but not the first one. The first one does not have access to plug in a charger.
Just to be accurate, I believe the old box with the two permanently joined cables and one empty port was just called the wiring harness. The 3 port and 5 port junction boxes refer to the new boxes with no permanent cables and the charge port.