Time that battery charge lasts dropped by two thirds after installing iOS ver26.

My iPhone SE2020 26.4.2 battery charge dropped from lasting 2-3 days to less than 24 hours immediately after updating to ver 26. I know that it sometimes takes a few days for things to settle after an update so I tracked it diligently for 2 weeks. It didn't recover. I checked all the usual culprits, battery health, memory, usage, etc, and nothing had changed from the last day I had ver 18 on the phone (I checked everything before I did the update so I had an accurate reference point). Help?