I didn’t know you could get a watch with more than 24 hours of battery life including GPS tracking (COROS APEX Pro). The accuracy is a bit weird though, the elevation chart doesn’t make sense.
I don't think it's that big of a deal for good running watches. I ran the JFK50 with a three year old Garmin 935 with a heart strap (HRM-Tri) in a little under 11 hours. My watch was close to 50%. That was with GPS updates every second. It would have been much better if I left it at the default, not the ultratrac or whatever they call the endurance battery mode.
It's really only been the last few years that running watches could last >24 hours with GPS tracking enabled.
I also have a Forerunner 935 which I've used for 24 hours, but I think I had it in ultra-mode where it takes GPS samples less often.
Before that I had a Forerunner 230 and I had to charge that mid race during a 100-miler, which was fun to do while running (used an external battery, put the watch and battery in a running vest while running one of my laps).
The latest watches which do 36 hours or more with full GPS accuracy are really amazing.
Apparently the reasoning is that what actually matters is oxygen partial pressure in the atmosphere, not true elevation. Measuring air pressure and reporting as elevation is a decent proxy for what athletes actually care about.
High-end Garmin watches as well. The fenix 7 can do 48+h including tracking, the Enduro2 will likely go 3 days.
And yes, elevation is bonkers, because GPS elevation via watch is about as precise as you guessing. (+/- 400 feet on Garmins, but I'm not sure there are any watches significantly better than that. )
I ran for 8:30 with my ancient Forerunner 235 and it still had some batteries left. Modern watches can easily do 24 hours, even the mid range Forerunner 255 can do 30 hours and the larger 955 can do 42 hours.
That's 36 hours of normal use, with a 60 minute workout[1]. My Fenix 6 lasts 8 days of normal use and currently tells me it can record a 14 hour run even with only 42% battery.
My Apple Watch with Cellular enabled is the only electronic doo-dad that I carry on my bike rides, even up to 100 miles. At the end of the night when it goes on the charger, I might have 20% left. That's good enough for me considering I seldom, if ever, leave the house with a phone.
And if one could ever get a cellular enabled watch without an iPhone, I'll be first in line.