Apple

I don't believe it to be accurate. Months ago, I turned off Optimized Battery Charging to see if I could "use it up" at all, nope.

Here's someone else in a similar situation, trying to get their battery health below 79%.

https://www.reddit.com/r/iphone/comments/zkhggx/trying_to_get_battery_health_to_79_percent/

Does anyone know if there's a reset on Battery Health, so however the Battery Health is calculated, it re-calculates from scratch?

This is the best info I've found so far...

https://www.reddit.com/r/ios/comments/a6ter0/reset_battery_health/

I had 84% of maximum capacity and I did a calibration of the battery (Charged to 100% --> draining all battery --> waiting 8 hours --> charged again to 100% waiting another 8 hours --> and a forced restart) and after the calibration the maximum capacity shows me 78%.

Not looking forward to that, but is what I'll be doing that unless someone knows of a software/ui means of achieving the same?

(I've been holding on to AppleCare+ for a full extra year until the battery drained to 79%, so I could then get the battery replaced. At this rate, I wish I'd let AppleCare+ expire. I'd assumed I could use-up 8% in a year, but it literally hasn't dropped a single percentage. I think it is stuck, and as soon as I let AppleCare+ expire, it is going to plummet.)