Use Low Power Mode to save battery life on your iPhone or iPad - Apple Support (HK)
How to Fix Bad iOS 13 Battery Life
Fix: iOS 16.3.1 Battery Drain Issue on iPhone (2023)
Massive battery drain with iOS 13.3.1, iPhone 7+ : r/ios
iApplebytes confirms iOS 13.5.1 has a worse battery life, geekbench 5 battery test is a intensive test. On my iPhone 11 i got around 9-10hours of screen on usage and on geekbench