How do I solve constant battery draining issue on my Apple Watch Series 9?

Same problem here. The watch is useless to me because I track fitness and sleep and it won't go an entire 24 hour period. The watch is only 1 1/2 years old and is under warranty with Apple care. I was at the local Apple store on 2 separate days for hours. They could not fix it and said my battery life is at 88% so they could not replace it. My capacity may be 88% but the battery goes dead on me, so it really doesn't matter. The problem did happen after my last update. I was also on the phone with Apple support and escalated it to a manager who escalated to a "super genius". I spend a long time on the phone with the manager, answered her questions and gave her access to my watch to get logs from it. She called back a couple of days later and said they needed more information. At that point, I had spent so much time on it that I had no more to give. Apple does not stand by their products, and their support is all determined by AI.

Did you already try to erase the watch and pair it again, setting it up as a new device?

Unpair and erase your Apple Watch - Apple Support

Did you already check this discussion from the time after watchOS 11 has been first released?

Watch os 11 update drains battery 30% fas… - Apple Community

Did you disable the Live Activities as well?