The Samsung phone I use these days has a "Protect Battery" mode that can be toggled (both manually and with automatic user-defined routines). It limits maximum charge to 85%. For those who want it: That's the ~same thing, without the psychological trick.

It also has some other settings that relate to smart charging that I don't fully understand (mostly because it's kind of inscrutable).

But the idea, AFAICT, is that it works with a person who charges their phone on a fairly regular schedule (they sleep at about the same time every night with plugged in all night).

The battery meanders up to 85% or something and holds there. Shortly before the person normally wakes up, it starts coming the rest of the way up to 100%. And then they wake up, unplug the phone, and it begins to discharge.

This helps to minimize the duration of being at a high state-of-charge, which is also a big factor in long-term battery longevity.

It's a tidy set of tradeoffs, I think.

Nice idea. I think the reason it's not communicated as such is that then companies would be expected to advertise time on battery when charged to 100%, not 125%.

Yes and yes.

I recently investigated large portable power banks (Jackery, etc.) and like that there are options to charge faster with a battery life tradeoff. Let people make their own informed choices.