On iOS 11.3 or earlier, my X used to give 4 hrs of screen time from 100% to 60%. With 8-10 hrs of total screen usage.
As of iOS 12 (all versions), my X (earlier 100% battery initially on iOS 12, now 97% battery) comes down to 60% in about 2.5 hrs of screen usage with a total screen usage of 5-7 hrs with similar usage.
My 7 met the same fate as iOS 10/11 progressed. Initially 8+ hrs and later barely 6. With a near fresh battery.
My mom’s 7 started with 9 hrs screen usage and is now down to 4ish with a 100% battery on iOS 12.
Many of these devices have been DFU restored and started clean without a backup.
Happens across every single iPhone.
Will happen to XS series as the year progresses. And so on.