It can do a health check, just requires 1 or 2 full discharge/recharge cycles.

It measures current consumed during the charges and compares that to the battery specs.

Over the years I've found it pretty accurate. I keep multiple phones of the same type with the exact same OS/app build out, and can see the difference in battery health between old/new, and see it reflected in battery life when using either one.

I keep phones forever, and run AB on them once or twice a year, and it consistently shows their health dropping. I lose about 7-10% health per year, and that's reflected in reduced battery life during a day.

One phone is down to about 40%, and even with Lineage you can tell. It can run for a couple hours before needing a charge, while the 83% health phone goes most of a day. Again, same hardware, same OS, same apps, same usage.

Yeah you're right, it guess the battery health based on prolonged usage. I'm not sure what you are looking for exists in stock Android ROM. It's very possible that info is restricted to the system, so apps cannot access it.

Let us know if you find something, I would be very interested.