I’ve had my watches set to muted since my first day with the Series 0. I legitimately didn’t realize until your comment that the watch has ringtones or notifications sounds.
May I ask why you would want to have sound on the watch just like your phone does? To me, that’s like half the point almost. To get notified without any sound at all.
I know it’s not ideal and Siri should be able to tell you or something, but you can open Find My on your watch and see a battery icon on all your devices. No specific percentage though, but it might just help our lazy asses when the phone is charging aaaaall the way over there.