https://wccftech.com/ios-15-4-battery-drain-test-video-reveals-significant-improvement-on-older-iphone-models/

Apple released iOS 15.4 to all compatible iPhone models earlier this month with a boatload of new forward-facing features. We are now waiting for Apple to send out invites for its WWDC event this year where the company will announce its forthcoming iOS 16, iPadOS 16, macOS 13, watchOS 9, and much more. Since iOS 15.4 is now out, some aspects need to be addressed or brought forward. Henceforth, an iOS 15.4 battery drain test will give us insight if the update takes a hit on the battery life of compatible iPhone models.

With every major update, there are chances that the battery life is affected on some iPhone models. For our ease, YouTube channel iAppleBytes have conducted an iOS 15.4 battery drain test on iPhone 13, iPhone 12, iPhone 11, iPhone XR, and older models. The exhaustive battery test will let us know if updating to iOS 15.4 affects battery life on all compatible iPhone models.