Optimised battery charging..

Hi all, having an iPhone 15 as a gift for about 3 months now, my battery setting is set to optimised battery. Never - and I mean never have seen the notification that optimised battery is on, each and every day I wake up and my phone is from 78 to 80%, you will ask me so I will say that again, my settings is on optimised battery not 80% limit. My location services (significant locations and system customisation are on) any help would be welcome.