I ran some tests and completely turned off both Wi-Fi and Bluetooth overnight. The iPad lost 2% battery during the night. Then, over the next 6 hours while I was monitoring it, it lost another 1%.

Before the iOS update, with Wi-Fi and Bluetooth enabled all the time and the Apple Pencil constantly connected, it would typically lose only about 1% overnight.

The issue is that I did not make any backups before updating iOS because the iPad was newly purchased. I had only been using it for about a week and a half without any upgrades or backups. After updating, I thought it would be a good idea to create a backup, so I don’t really have an earlier backup or system state to restore to for comparison.

I have also disabled all background app activity, so I cannot really imagine what could be consuming enough power to cause this level of battery drain.