Remaining battery life estimates for an activity don't seem to be accurate.

How old is your watch? How heavily do you use the battery and need to recharge? Do you recharge to 100% often?

If the watch is old and heavily used in terms of battery charging then 100% today is likely not the same capability as 100% one or almost two years ago. Maybe 100% today is now only 90% of the original spec and 60 hours estimate should also be reduced by 10% to 54 hours.

Unfortunately the watch does not understand battery degradation and still believes that 100% battery = 60 hours of GPS run time.

My own 6X Pro Solar was exchanged after 15 months and I always treat the battery with sympathetic charging - usually to only 80% once per week and running it down not below 20%. Even so I felt that the battery was not performing as well as when new and the replacement watch (brand new, not refurbished) restored full battery performance once again. 

The watch is year and half old and I charge it roughly every 2 weeks, which means I went through about 40 charging cycles. What the point of giving me estimate in hours if it can't be accurate due to the battery degradation. If Garmin wants that feature to be useful it has to self-calibrate. And even if the battery capacity degraded by 10% after only 40 charging cycles, which I highly doubt, that still doesn't explain the 40% increased burn.

Anyway, I realized that I was using live tracking during the run, so perhaps that had affected the discharge rate, but again, it is surprising to have had so much impact. I guess I need to do more experimentation.

eezytiger said:

I've seen a run rate of 1.7% per hour subsequently on other GPS + GLONASS activities.

That is very close to the claimed 60 hour estimate for the full battery. Thanks for confirming. Did you do anything special to get this information in the FIT file? I looked inside one of my FIT files with two different viewers and didn't see anything that looked like the battery discharge info.

DCRainmaker Analyzer is able to pull the battery data from the fit files. 

I bought mine on 04.11.2019, they replaced mine three times with brand new ones because of broken buttons - first replacement on 07.05.2020 - mechanical problems with start and back buttons; second replacement on 21.04.2021 - watch became unresponsive when start button pressed; on 03.06.2021 start and afterwards up button became unresponsive when pressed. Got the new - brand new - on 08.06.2021. Let’s see how long will last this one. All previous 3 fenixes were scratchless, never banged against anything, really taken good care of. Battery-wise - so far zero problems with all units. Warranty expires on 04.11.2021, this fall, so hopefully the one I have now will last normally and won’t break down. 
Edit: I have 6X Sapphire, always running latest stable software, never installed any betas.

I think (don't know for sure) that maintaining a phone connection beyond normal smartphone notifications is likely to increase battery drain. I think I've read this for music control from watch to phone. Maybe it is true for live tracking too. That's not a feature I've ever used. 

silentvoyager said:

What the point of giving me estimate in hours if it can't be accurate

Estimate - roughly calculate or judge the value, number, quantity, or extent of.

Accurate - correct in all details; exact. 

False marketing claim - when you you know your estimate is always at least 50% longer than real life measurements 

The only activity where I do get correct estimates is indoor walk/runs with a single data page. No GPS and not a single click on the watch for the whole activity. Other than that the estimates are always waaay more optimistic.

silentvoyager said:

live tracking during the run, so perhaps that had affected the discharge rate,

Yes! Constant communication to your phone so of course it would greatly affect battery consumption