Some users are complaining about reduced battery life on their devices after updating to iOS 15.4. So, the iPhone 13 Pro Max now works without recharging for only half a day.

 iOS 15.4 includes 39 vulnerability fixes. 

According to user speculation, Apple has started to use ProMotion's 120Hz maximum refresh rate more frequently.

Apple released iOS 15.4 in March. The update includes the ability to unlock iPhone with Face ID while wearing a mask. 

Installing a new OS on an iPhone runs a lot of things in the background, from indexing to battery recalibration, and it can take hours or even days. The process consumes energy, and recalibrating the battery may give the impression that it is draining faster, when in fact it is not. Plus, there are updates to many applications.

Users are advised to wait a few days while the battery is recalibrated. Most likely, the battery life will return to normal. However, it all depends on the age of the smartphone. 

You can monitor battery performance by going to Settings > Battery > Battery Health. 

iOS 15 is compatible with all the same iPhone models as iOS 14.