Apple released the iOS 11.4 update late last month. The update included many new features and changes, but it appears to have also brought along a serious problem. A large number of those who updated their devices to iOS 11.4 are complaining about rapid battery drain. There are several threads discussing the problem on Apple's official forum, and on one of these threads, close to a thousand users have confirmed the issue with their unit. I have the same issue with my 6S+. It was fine before the update. And my battery health is at 90% yet I just watched my battery % drop from 50% to...
Source: https://www.gsmarena.com/ios_114_users_reporting_rapid_battery_drain_post_update-news-31620.php
