Battery drain even when switched off

Hi Team,

I am using Iphone SE 2022 with IOS 18.0.1 with a battery life of 89%! I had fully charged my iphone by 12AM and switched off the phone immediately.. Woke up the next day powered it on I notice a surprise battery has dropped almost 50%!!!

Why does the battery have to drain 50% when switched off!!! Lets assume that iphone still uses some services in background when switched off even then 50% usage is not justified (Please note I have already turned off all the background app and turned off location service) !!

Has Apple programmed the battery life with time!!!???