iPhone 12 running iOS 18.5 is overheating and draining battery rapidly

Post the screenshot that shows battery usage by apps along with the graph. Apps update in the background by default and unless you pay attention to the little blue dot that appears next to the app icon, you have no idea it has been updated. Some may introduce bugs that will cause problems.

Also, after an update I recommend to do a Force Restart to clear any remaining cache files. It may take a couple of attempts to get the speed and sequence of the key presses correct:

• Press and quickly release Volume Up
• Press and quickly release Volume Down
• Press and HOLD side button until Apple Logo appears. It may take up to 15 seconds before you see the Apple Logo and you want to ignore anything else you see on the screen during that time. It that Apple Logo does not appear, try again.

Hello,

With any new version of iOS there are always maintenance and reindexing tasks to be performed. It should settle down in a few days.

1) Have you tried a restart?  If not, do it now.

2) Go to Settings > Battery > BATTERY USAGE BY APP to see the apps that are consuming your battery.

3) Check “Battery Health” in the link: 

iPhone Battery and Performance

Good luck.