This week I had to reset my watch to factory defaults because a few of bugs.
First of all, I'm always a long way from reaching Garmin's battery life limit.
As a good case, I had a trail running race 9h30 between 1600 and 3000 of altitude under 100% sun.
Activity mode with All Systems mode and wrist-based heart rate ==> Up to 34 hr. with solar from Garmin website.
The result is 50% depleted after 9h30!
Activated a course to get ClimbPro, this is the only screen in my race.
There is a gap between 19 and 34 hours!