Many iPhone users have complains of severe battery drain in iOS 11.4. The latest iOS is reported with poor battery life after users upgraded to latest iOS11.4. The battery life is very poor in ios11.4 as the battery drain really fast. The battery drain is very surprising in many cases as it happens to be like 10% in 15 minutes only.
Almost all iPhones including iPhone X, iPhone 8 and iPhone 7/6 have been reported to get affected with poor battery with upgrade to iOS 11.4. It's possible that the 11.4 broke some application and that application is using the location services more than it needs to. You could try to disable access to location services app by app and see which one is the one using it constantly. Sometimes the battery drain is immense and consumption is too high by system applications.
How to fix poor battery life in iOS 11.3/iOS 11.4:
Go to Settings -> Battery usage and check which apps are consuming tom much memory. See if you can do anything about this. In most of the cases application like Facebook, snapchat consumes too much battery and data after upgrade of iOS. You can try re-installing these apps to latest versions to fix any memory leaks. Or you may try following fix’s :
Fix 1. Turn off iCloud Drive sync: Change the iCloud setting to turn off the sync as this is major battery consuming take (like photos, video upload). Please check that any major cellular updates are also turned off.
Fix 2. Turn off Siri & Search indexing in Photos - to minimize the "risk" of lots of background activity that might drain the battery. It is quite possible that iOS 11.4 will be reading in the background the photos to try indexing and clustering them in order to offer better search options
Fix 3. Try setting Auto-Lock to a new value:iOS system update might have set Auto-Lock to Never so the screen never turned off.
Fix 4. ResetGeneral settings: Clear the safari history. Turn the iMessage off for about 10 seconds then back on. Now Goto-> cellular settings and toggled ALL settings either off then on or on then off again depending on how they were originally set. Now hard reboot the iPhone and check the battery performance.
Fix 5. Turn Off unnecessary widgets/application: it is always recommended to disable any unnecessary widgets lying on your lock screen. You can also consider disabling Raise to wake feature and optimizing screen ON time etc.
Fix 6. Buy a Battery case or cover: You can consider buying battery cases from out recommended list as they are good power backup in case of emergencies.