Di2 battery issues

Hi Folks,
Looking for some tips as I’ve had no luck personally or with 2 bike shops. I have XT Di2 on my CX bike and I find the battery goes flat when not removed from the seat post and unplugged.
I’ve tried problem solving by leaving the mech unplugged, then the Junc A box…but still find the battery goes flat. Both shops tested and could find no fault and said a firmware update was required but looks like it could be the battery. Bought a new battery and still have them same fault!
So it has me thinking the only fault could be in the Junc B box which is in the downtube and means you have to remove the BB…which would need to be replaced. Anyway, would appreciate any inputs and if others have had B box issues?


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I had a similar issue with my battery randomly dying way too soon. After lots of trouble shooting, I took it to a different shop that told me they had a program that could check every point in the system and there was a problem with the connection in one of the shifters. They replaced it and no problems since. (Sorry I don’t have more details, it was a while back and I’ve forgotten the specifics)


Appreciate that input! Hadn’t considered the shifter drawing power…makes sense that it could be constantly using the batter. Also very exposed to the elements in cyclocross! I’ll do some testing on that.

Thanks again!

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Also check your derailleur set up. It’s possible to set the limits wrong such that the motor is pushing against the stop and drawing constant power. And/or don’t leave your bike with the chain the the largest or smallest rear cog.


Yeah - if your shop has the SM-PCE02 (and they should, really), then they can use that to run battery usage diagnostics using E-Tube Project V5 (or V4).

This will only find battery issues on components that have firmware. So that’ll be the FD, RD, Junction A, and Battery. It cannot detect issues like damaged wires, Junction B, dirty/corroded ports, or anything like that.

Do you also have a display or a wireless module on the bike? Does it go to sleep when you’re done riding the bike? If anything is keeping the bluetoothLE/ant connected, then that could be the problem.

While incorrect derailleur limits can definitely cause the derailleur to draw more power (or fail to shift), this is only the case when the derailleur is moving. Once the derailleur has completed the shift or has given up and shifted back to the previous gear (when limits are set incorrectly), it should no longer draw power.


Thanks Terry,
I don’t have a display, just the red light/green light SM-EW90-a junc box. I don’t see any lights on so assume it is asleep.
I think I’ll do the rounds and find out who has and uses SM-PCE02 on a regular basis. It gets kind of annoying having to insert and remove the seatpost battery all the time - Also the fear of riding and the battery may go flat.

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Yeah, that’s a bit frustrating. These systems are great when they work well, but they can be a bit tough to troubleshoot.


Hi Terry,

Just by way of an update. Got my bike back from the shop. I got in touch with a shop near by and asked if they had Di2 testing kit and they did. Anyway, dropped it off and got it back in less than 2 weeks. Received video updates of the repair which was really interesting. Turns out the BB was sitting pretty damp - it is a CX bike. This mean the B Junc box was also susceptible to water ingress. You can see in the picture the adapter has lost its male pin. Anyway, that’s been replaced, 2 cables, BB and a new chainring…bikes eh! The mechanic moved the B box to the seat tube so it is out of harms way as well.

Anyway, I can now store it indoors without removing the seat post after a ride. Result!

Thanks for your input.



Wow, that looks nasty! :slight_smile:

Good to hear it’s fixed though! Thanks for the update!