Originally Posted by
Steve B.
I have noted though, that using BT on the Di2 battery in a constant link to the Garmin while riding, does use up DN110 battery life, when it went from 100% to 90% in about 5 riding hrs. (As displayed on the Garmin) Not linking BT to the Garmin showed no add’l battery drain over the next 5 hrs.
Its the same as any computer. Leave the bluetooth on, on your phone and it will eat batteries also. Its a service that is running on your bike. It's great if you want to connect to the Shimano app or connect to other devices but otherwise its just going to sit there being a battery hog.