The constantly on screen in the new Apple Watch did not affect the duration of the work
So, according to most reviews, the Watch Series 5 holds about the same charge as the previous generation watches. The Verge writes that the new watch lasts about the same as the old. That is, they are enough for the day of use (about 18 hours).
Autonomy when using the new feature provides one important feature. In normal mode, the Watch Series 5 screen has a frame frequency of up to 60 Hz. In Always On Display mode, it decreases to 1 Hz, which reduces the load on the battery.