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 20% in a matter of minutes while not using it. I’ve looked through all the settings and can’t see anything I’ve previously had turned off turn back on with this new update in regards to saving battery life. Whatever it is that’s causing it they need to fix it ASAP
The problem seems to be independent of the iPhone model being used. As for workarounds, switching off the Wi-Fi worked in some cases, while connecting to a 2.4GHz Wi-Fi network (instead of 5GHz) did the trick in others.
However, several other users said none of these worked for them, so many of them rolled back to iOS 11.3.1 which made the battery life normal again.
For its part, Apple hasn’t yet offered any official word on the matter, but we expect the problem will be resolved in the next iOS update.