I managed to run my battery from 100% to automatic poweroff in 5 hours. But it was intentional.
I did this with All Systems + Multiband, pulse ox enabled, and 100% backlight with "no timeout".
I knew a practical hiking mode like Auto Select (SatIQ), pulse ox disabled, and no backlight would run for about 20 hours. I didn't really know that I could make it so much worse!
The motivation for me, as an impatient data nerd, was that I wanted to log the time intervals it takes to descend through each reported battery percentage under a relatively steady power drain, so I can tinker with some correction factors in my own personal watchface app.