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.
