Updated iPhone X to iOS 16 and have seen a significant drain on battery.

Give it a few days. After an update the phone needs to reindex content. To speed it up leave it plugged in, preferably overnight. And make a habit of doing so, if you aren’t now. The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates. Here's more information→About Optimized Battery Charging on your iPhone - Apple Support

Give it a few days, After a big update like this the phone is busy reindexing. this can take up to 7 days in my experience. My 13 started behaving normally in day 3 after the update