Can the Garmin Edge Drain a Di2 Battery?

I have had a bit of a nightmare these past few weeks. Got myself a 105 Di2 upgrade, but less than 1 year old and the system would drain out within 48-72 hours, even if I wasn't riding the bike. Took the bike to my local LBS and said, the only thing I'd noticed was a warning message for the left shifter battery, which is strange as they should last up to 4 years. Thought nothing of it. The LBS also identified the left shifter as the component causing the drain and as the components were still under warranty, they sent it to Shimano tech for inspection.

Shimano tech said the shifter was working as expected and requested the RD, FD, Battery and Right Shifter be sent in too. They said it was the main battery that was faulty, odd? Updated the firmware on the components and sent LBS, who ran tests and sure enough, no drain at all - all batteries showing 100% - this process however took nearly six weeks, six weeks no bike :-(

So I eventually get the bike back, very happy. Went home and then this is what happened, step by step

  1. Got the bike home, as said above, happy
  2. Charged my lights, charged my Garmin Edge 830
  3. Put the lights on the bike
  4. Put the Garmin Edge on the bike
  5. Turned on the Garmin Edge, immediately greeted  with an alert 'critical battery, left shifter'. W?!
  6. Checked the Di2 Screen on the Garmin Edge, left shifter RED, right shifter OK, gear at (80%, 4 out of 5 bars) WTF?!
  7. Checked 'maintenance' on Shimano E-Tube Project app, same as Garmin Edge status above 
  8. Switched batteries from right to left shifter, vice versa. No change on Garmin Edge, no change on Shimano E-TUBE project. WTAF?!
  9. Checked actual shifters by using the shift levers, left solid red light, right solid green light
  10. Has to be the Garmin Edge. So I removed the Di2 sensor from the Garmin Edge
  11. Checked the shift levers again, same as before, left solid red light, right solid green light OMG WTAF!
  12. Removed the batteries from both shifters, put the right batteries into the left, vice versa
  13. Checked the shift levers again, left solid green right, right solid green light
  14. Checked Shimano E-TUBE app, both green, great.
  15. Disconnected the battery in the seat post, to reset system
  16. Updated firmware on Shimano E-TUBE app
  17. Ridden into work and back today c60km, its been 48hours since doing all above
  18. No sign of battery drain at all on Shimano E-TUBE app
I don't know how the Garmin Edge was creating this death loop with the left shifter and the Di2 system, or even if that's technically possible, but it must have been the root cause. I have no doubt whatsoever if I'd have left the Garmin and Di2 connected I would still be experiencing parasitic battery drain over the next 48-72 hours, would have been on the phone with the LBS again, taking the bike back in without the Garmin and we probably wouldn't have been any wiser. 
Does this make sense, as this is what happened to me. I'd hate it to happen to anybody else or am very keen to see if its technically possible?!

  • I assume your Garmin is turned off between rides. Can't see how Garmin can cause a drain on your Di2 if it's not connected. Garmin could possibly have an erroneous battery level report. Could be contamination on the coin cell battery causing a poor connection.

  • Definitely not the coin cell batteries, Garmin turned off yes, but the drain was real, could not shift. No issues now at all since removing Di2 from Garmin, has to be some kind of communication error being passed one way or the other. 

  • But you solved the problem by swapping batteries L to R and vice versa so the drain on the coin cell wasn't real despite showing up on the shifters themselves. Doesn't sound like a Garmin problem to me.

  • A week ago I connected my Garmin 530 to my Di2 and I’m suddenly having to charge my di2 after 3-4 days and only about 15 hours of riding.  My bike is only a year old and has not been used that much. I’m not very technically aware with my bike parts etc but I think I’m having the same problem as above.   So maybe it’s not my battery but the connection with the Garmin?  Which was turned off by the way when not in use. Obviously. 

  • My coin cell battery life however remained as full no change . Just no life in the shifters.  I went  today from 45% to 27% on the main derailer D12 battery on a 2 hour ride.  I untill now I have had no issues with battery life 

  • I really recommend removing the Di2 Sensor from the Garmin Edge, I’m convinced it sends the system in to parasitic drain. Use the Shimano E-Tube app or  Di2 shifters/derailleur to check for battery level - I’ve had no issues whatsoever since removing. Please let me know how you get on, good luck!

    you might have to reset the Di2 and update firmware too if issue persists. 

  • I will thanks.  And I’ll post back after testing it