Battery drain on iphone 11

i’ve been using my iphone 11 for about 9month and battery health is still on 100% and im on ios 14 but recently i left my phone on standby overnight around 6-7 hours then when i woke up it drain about 12-13% of my battery. I turn on my flight mode and also off background refresh and also i close all the apps before sleep. Why does standby consume alot of battery ? is it because my battery is faulty of something or it’s because of ios 14 ?