Please join me hereI think it's the OS. My 7 Plus did this when I had the 7 Plus back then on iOS 10. My 8 Plus does it and so does my iPhone X. I don't use wireless charging, so this also happens even if wired too at 90% so it's normal for your stats to reset at 90%. I also use this gauge this to see if I have an issue with usage and standby going up at the same time. If it doesn't then I'll plug it back in and charge it to full (never had issues and my battery capacity is still over 100% on Coconut battery). Oppose to fully charging it only to find out that my usage and standby are the same.
https://forums.macrumors.com/thread...-minutes-used-shall-we.2126211/#post-26215538
I need people to do this exercise if they dont mind. Thanks