The Garmin Fenix, lasts over 2 days at a minimum, and with the no-pulse-ox configuration can last as long as 3 weeks. I find with about 10 hours of exercise I charge it at most once a week. The tradeoff is that to get GPS tracking you need to put it into activity mode. But even with GPS off there are a ton of useful metrics - heart rate, step counts, calories, sleep tracking.

I have disabled all the smartwatch notification features though, I don't want the distraction, I just want to measure/map my exercise.