Optimized Battery Charging not working on my iPhone SE running iOS 18

iPhone SE 3, iOS 18.5

'Optimised Battery Charging' ON in 'Battery'.

'Location Services', 'System Customisation' and 'Significant Locations' all ON.

My home shows as a 'Significant Location'.

Battery max. capacity is 90%.

Apple 5v, 1A charger.

I've tried shutting down the phone and restarting but this doesn't appear to have made any difference.

Overnight charging has usually happened at home from about 9 pm to 6 am, most days. Optimised Battery Charging (OBC) notification has, in the past, appeared on the lockscreen and charging to 100% was usually completed by about 3.30 am.

OBC hasn't worked reliably on my phone for a while, not just with iOS 18.5.

The phone was originally on iOS 16 and has slowly been updated until 18.5 on 13th. May.

iOS 16 worked quite well, 17 slightly less well but still acceptable. Once updated to iOS 18, OBC has become steadily less reliable. Now, when put on charge, the battery level steadily rises to 100% over a period of about 2 hours. I've started to keep an eye on the charging and disconnect when charge level reaches 85 - 90%.

I've read that, despite OBC being ON, sometimes the phone needs to charge to 100% to check calibration. That'd be fine if it WAS only occasionally but, since it happens every day it's not acceptable.

Can anybody suggest a solution?

I must admit, I don't really like OBC and would much prefer the ability to set a simple charge limit of 80% or so but that's not possible on my phone.

[Re-Titled by Moderator]