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.
Find my iPhone is still active when powering off the device, could be that? Which version of iOS are you running?