My OG Ultra lasts 3 days if I turn off the always on display, which I do because it doesn't serve much of a purpose, I can just tap the watch to wake it. It charges from 0 to full in 1.5 hours, pretty linearly, so dropping it on the charger for half an hour or an hour while I'm on a work call every other day or so keeps it plenty charged.

This one will have even more battery life, and gets 12 hours of use in 15 minutes, which I suspect will mean for me without the always on display I may well be able to charge it only while I'm actively in the shower (when I'd take it off anyway as I hate wet bands) and be good for the day.