What can be the reason that an iPhone SE 3rd gen. loses battery power significantly over night when it is completely shut down? The flight mode was activated before the shutdown. The device is brand new, battery capacity and health is on 100%, no background tasks are allowed. It is a replacement for the same model, which had the exact problem some weeks ago.
If it’s brand new, it might be doing stuff in the background. I had a similar issue some time ago but eventually it went away.
Maybe some buggy app is causing it. Might be worth setting up as new instead of restoring from a backup.