iOS 11.4 Battery Drain Fix
I wanted to post my issues and solution to the Battery Drain issues after upgrading to 11.4. Hopefully this will help some. I did the 11.4 upgrade on my devices including an iPhone 6s, X and iPad Air2. the Air and 6S experienced severe drains, going from full charge to almost zero overnight, sometimes complete drain. The iPhone X was fine.
After waiting, restarting and other troubleshooting, what finally alleviated the issue was resetting my network settings. Go to network settings under Settings > General > Reset > Reset Network Settings. After this you will need to add your Wifi networks again. This should solve the drain issues.
iPhone X, iOS 11.4, iPhone 6s and iPad Air2