Shortly: iPhone users eagerly await Apple’s release of iOS 15.4 for the additional ability to use Face ID while wearing a mask. However, in the days following installation, a small number of people reported a reduction in battery life. Apple has now issued a fix.
With the release of iOS and iPadOS 15.4.1, Apple says it fixed an issue that reduced battery life on some devices after installing version 15.4. The latest update also includes fixes for braille and hearing aids. Even users who have not had any problems with the battery life should still install it for the security updates.
Some users reported that the battery life on their iPhones dropped by up to 50 percent after installing iOS 15.4. Initially, Apple Support tweeted that some issues were to be expected in the first few days after firmware updates, but some users had reported reduced battery life of more than 48 hours after the update.
Some theorized that the problem with high refresh rates in iPhone models is related to ProMotion, but reports have not been limited to these models. Others suspected it might have something to do with aging batteries. In any case, fixing the problem with an update confirms that it is a software issue.
To update your iPhone or iPad, go to Settings > General > Software Update.
https://www.techspot.com/news/94028-apple-firmware-update-fixes-ios-154-battery-life.html Apple firmware update fixes iOS 15.4 battery life issue