We need to talk about battery lifespan

[Skirmisher]

Not me.  This is why I'd like to see user-configurability.  I had a "phone" that did the 80% charge then discharge to 20% thing.  Nothing in the world as frustrating as charging something overnight to have a dead battery in the morning so that the battery could last 10 in stead of 8 years in a device that's only useful for 5.

You may be exaggerating, but you're blowing this out of proportion. We can have more sophisticated behavior than "charge to max level, then never charge again until reaching min level". At any rate, batteries these days are only really lasting 2-3 years. In the last 3 years, an obnoxious number of Android phones in my household (often acquired used) have been exhausted of useful function because the battery performance became untenable. My Dell laptop from 2018 only has 38% of its original capacity; I only even know that because Plasma bothers to display this in the battery tray panel, I would only have had vague feelings of worse runtime had I not known that info was available to me. Handling charge behavior intelligently is critical to combating e-waste and extending longevity of devices where the battery often limits the lifespan of the whole unit.

I know you said you wanted to see it configurable. I know that it's less of a problem when you're not using a mainstream phone and can replace the battery. I still feel that you're needlessly hostile to this concept being on by default for the benefit of users. This perception that it's a bad idea to use less than the "maximum capacity" of a battery needs to change, and it can be done without compromising the overall user experience of the device.

I fully expect cars will be this way if everyone has electric cars.  The power companies are all planning to use your car for load leveling.  Charge all night, but your battery is dead because you went to use your car three hours earlier than you normally do, and it was really hot last night so everyone's air conditioners were running.  (Of course, I have bigger doubts about our power grids being able to support large numbers of electric cars anyway.)

Besides the technical and other hurdles that would need to be overcome before this becomes a possibility, there are much better ways to load-balance the grid with a network of batteries that don't involve putting the entire capacity up for grabs. And the calculus involved for car batteries is quite different from what we're dealing with here.