I’ve been trying out what happens with body battery when using the index sleep monitor with compatible and non-compatible devices. Here is what I’ve found.
When I first activated the ISM, I had my Descent Mk3i set as primary wearable and training device. The ISM would work as advertised except that it would not provide any body battery information. That clearly seems to be a bug.
Next I added a Forerunner 965. It is one with a cracked screen due to a crash that my wife had, so not a device that I plan to actually use. This did not yet help, but it did once I made it the primary wearable and training device. This is what I now get:
The ISM provides body battery data. (It has an odd behavior where at some point during the night it stops accumulating and goes flat. I’ll see what happens tonight.) It provides rest and stress info and body battery. The data shows up on the Connect app. It also shows on the Forerunner. It does not show on the Descent, but other data does, such as detailed sleep data, training readiness, etc.
At this point I thought I would need to wear the ISM continuously except when I use my Descent for sports. However, I found that when I wear the Descent, it will provide body battery data back to the app, the ISM, and the Forerunner. The Descent would not show the same body battery number, because it misses some historic info. Today it was 5-6 points higher. However, the continued trend on the app (etc.) matches what is happening on the Descent. The offset of 5-6 points remains consistent. To me this suggests that I can alternate wearing the Descent and ISM and on the app I will see the right body battery data informed by both devices. The only missing part is the body battery data being synchronized back to the Descent. Hence I need to look on the app to see proper body battery data, whereas the Descent will give me an estimate based on incomplete data.
Once the bug that prevents the ISM from providing any body battery data unless I have a Forerunner 965 or similar activated has been addressed, I plan on continuing with just the Descent Mk3i and the ISM.
It is odd that a current top-spec model with features and hardware that well exceed the Fenix 8 is not having body battery true up. I hope this will also be addressed soon.
