Since moving to the iPhone XS I’ve been seeing the low power warning pretty much every day. It was way worse than my X. I’m glad to report I’m getting through a day again, all by turning off screen time.
(How to: go to Settings, screen time, turn off screen time).
This has made a difference to my day to day experience and I feel the XS is back on par with my previous X.
If you’re having battery issues on iOS 12 try doing this setting change and turning off screen time.
Let me know how you get on.