It has been on iPhones for quite some while, but on androids even longer. Before that it was in the form of some smart charging scheme that it would only finish charging until the moment it thought you would unplug it.

It makes a bit of a difference, but not dramatically: https://youtu.be/kLS5Cg_yNdM?t=3m26

In that experiment, it’s also unclear if the 30% lower limit or the 80% upper limit is more important. I suspect the former.

I charge my s25 to 80%. Previous phone (pixel) was also limited to 80%, but radio stopped working after 2 years so I had to buy a new phone.

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.

As do iPhones. I expect all flagship phones these days have the same ability.

On Pixels too.