My Apple Watch is now so old that it’s unsupported by new WatchOS, but the battery still lasts a day without problem. It probably helps that I disabled the always on screen. Lasting all day has never been a problem, though.
Do you use it for workouts, especially for longer periods everyday? I’m a constant Apple Watch user and workout everyday, but I do find the battery life lacking when I’m out on hikes for a few hours. My watch is only a few years old and is supported for watchOS upgrades.
My guess is that the sensors use a lot of energy (even when the display is normally off) and that the longer one uses it for workouts within a day (with the sensors continuously on [1]) and the older the watch is, the lower the battery life.
[1]: there is a setting to in the workout app to reduce the frequency of GPS and heart rate readings during walking, running and hiking workouts when low power mode is also turned on
