I cannot agree more. The battery not even lasting a day is what prevents me from using it. When I want to go for a run with it, it's always out of battery.
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