... Aren't devices designed to only charge the battery to 90% (and report that as 100%), because actually changing a battery to 100% is pretty harmful for it?
You're thinking of cars, industry and others that have high value batteries.
Power tools, smartphones etc charge to the maximum 4.2V/cell, sometimes even 4.3V (some chemistries safely allow it) because the average person just wants the maximum runtime and will replace the equipment before the battery degrades significantly.
This sounds like the battery and the charger's problem to handle, not mine.
All this tech, all this automation for every damn thing, and people keep coming at me like I'm supposed to do everything manually with my fingers and eyes and maybe an alarm or something to keep me on schedule. No. Stop it.
Make the charger handle it, or shut up. Make the phone, the charger, and the battery handle it together, you know, with digital automation. Do not even mention it to me.
All BMSs I've come across have this disabled by default sadly, manufacturers seem to target longest device runtime, rather than extended battery longevity
On my FP3 it needs to be enabled in a terminal, while rooted (newer devices have it in the settings).
On my Steam Deck it also needs to be enabled in a terminal, the exact command differs depending on the model of steam deck. An embedded developer or tinkerer will find it very quickly in the kernel sysfs though.
Edit: Apple and Lenovo are the only companies I'm aware of, who have historically cared for the internal batteries in certain models of their laptops. Macbook Pros in particular used to behave differently when they reach 90%, some will stop charging and others will wait a few hours then resume charging to 100% depending on how the machine is used. I assume this is the only reason why my 2012 MBP still is going great on its original battery, running Linux of course.
Lenovo used to let you configure the charge preferences in the BIOS of their ThinkPad line
This was a decade ago though, can't vouch for whether this applies to the modern stuff too
