The Series 10 is confirmed for 18 hours, like the Series 9 before it. The Ultra will definitely last longer. The Series 9 can as well, if you turn off features

The Series 10 is confirmed for 18 hours, like the Series 9 before it. The Ultra will definitely last longer. The Series 9 can as well, if you turn off features which Apple advertised the Apple Watch as having, and if you do not record a single exercise throughout the day. If you use the watch how it was advertised, it will last ~18 hours, which means if you charge it overnight, wake up at 7am, are awake for 16 hours, it will not survive the night. Its not helpful, productive, or useful to state that you turn off headline features people paid to have in order to get greater battery life than even Apple advertises the device as having. Please adjust your discourse and do not repeat your behavior.