Apple recently released the iOS 12.3.1 update to fix some bugs related to VoLTE and iMessenge. But it looks like Apple is doing more than that, with iOS 12.3.1 also helping to increase battery life on older iPhone models.
YouTuber channel iAppleBytes performed an experiment to compare the battery between iOS 12.3.1 and iOS 12.3 on older iPhone models from 5s to 8. The results showed that the duration of the iPhone 5s / 6/7 improved. significant after updating to iOS 12.3.1. Specifically, iPhone 5s / 6/7 running iOS 12.3 version have battery life of 2 hours 35 minutes, 2 hours 34 minutes and 2 hours 58 minutes, respectively. When running iOS 12.3.1, iPhone 5s battery life increased by 14 minutes (2 hours 49 minutes), iPhone 6 increased by 18 minutes (2 hours 52 minutes) and iPhone 7 increased by 18 minutes.
However, after upgrading to iOS 12.3.1 on iPhone 6s / 8, there is no difference in battery life.
Note: iAppleBytes performed this test on devices with fairly new batteries and performance stability was not enabled. First, the machines are running iOS 12.3 and are tested until the battery runs out. They were then charged, updated to iOS 12.3.1 and running again. iAppleBytes uses Geekbench 4 application.
Please watch the video below to better understand the testing process of iAppleBytes.