Ek21

I charge the Ultegra Di2 with the charger that came with the bike, connected to a wall socket. I have read the threads discussing a recommendation to rather charge through a USB port on a computer, however, I am still interested to hear your take on the below:

1. Battery has some power left, still, I charge it as per above and remove the cable from the junction unit when the charger’s light has gone out, indicating a full battery.
2. A few days later, I take out the bike for a ride only to find out that the shifters are dead with no response.
3. I go back inside, connect the charger and verify that the junction indicates 25% battery level. I straight away remove the charger, goes outside and voila, shifters work flawlessly during a 1 hour ride. Back home, junction still indicates a 25% battery level.

This scenario have occurred multiple times. It seems like 1) the battery cannot have been (fully) charged and 2) plugging in the charger seems to make the system spring back to life.

Any guess on what is going on here, and how to solve it? I am asking since charging via my computer is not as convenient as through the wall socket.

Barry2 

My Di2 charger requires 5V 1A input.
I can't use some phone USB chargers, they don't output enough current.

Is it possible you didn't "disconnect" prior to unplugging from E-Tube, I hear that will cause the battery to drain.

Barry

Ek21

I have never used E-tube in connection with charging, if that is what you are referring to? I try to avoid that dreaded app, remembering the common problem that it busted the Di2 system upon initial setup. 😅

TerryDi2C

I'd have the bike checked by a bike shop. The SM-PCE02 tool can run (1) battery drain diagnostics and (2) determine whether or not the battery is on its way out.

Ek21

Ok, thanks, I will keep that in mind if the issue persists. Battery is only 2-3 years old, but you never know.