Hi my friend. i had/have exactly the same issues with my last 3 iphones. it feels like a programmed scam, so that you buy a new shitphone. Everytime the same shit. everything works fine. Making the „new“ update, battery drains in highspeed time. Note that the battery life before every update was good! same issues like your description. Believe me i tried every „magic“ trick that you can find in google/apple forum. Nothing helps. In my opinion this is a scam. It feels like you get scammed.