We need to talk about battery lifespan

[diodelass]

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.

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.)

Okay, so we're definitely not on the same page here. Your post describes two very different concepts, neither of which was the one I presented in the initial post. On a re-read, I think some of what I said may not have been entirely clear, so I'll attempt to sort it out a little:

In addition to being able to control maximum and minimum charge levels for their batteries, some laptops (again, namely Thinkpads) can also set up charge hysteresis, which makes the charging stop at a much higher threshold than it starts - usually stopping at 75% or so, and not resuming again until the battery charge level falls below around 25% to 40%. This is not what I was talking about in my initial post. Charge hysteresis is intended to prevent laptops that spend most of their lives plugged into their chargers from wearing out their batteries through many small charge-discharge cycles; since the laptop itself is usually powered entirely by its charger in such a case (and not by its battery), the battery only loses energy to its very slow self-discharge, and it may take many weeks, even months or years, for the charge level to drop all the way from 75% to 25%. Contrast to what happens if the charger kicks in promptly at 99% and returns the battery to 100%; this can result in many small cycles per day, which take their toll. At any rate, this makes very little sense to employ on a device like a phone, tablet, or sub-notebook, since those devices almost always spend most of their lives off-charger, so this is not what I intended to promote in my original post.

What I am talking about is much simpler: I just want to narrow the charge and discharge limits of the batteries. When I leave my phone charging overnight, I want it to be at 80% when I wake up the next morning, and not 100%, because the 100% threshold that today's vendors have selected is excessively high and intentionally damages the battery. In fact, this would not even need to look like 80% to the OS, and the charge levels could simply be redefined so that "100%" is now the same level that most vendors prefer to call "80%". De-rating components like this to gain additional longevity is an accepted practice for almost every type of electronic component; you may recall that it's especially important for electrolytic capacitors, which are vulnerable to ongoing degradation when operated near their rated limits. It's even more important for lithium-ion batteries, which are very chemical, very unstable structures that are prone to several different modes of decay.

The only drawback that users will experience to having their charge capacities reduced is a ~20-40% decrease in runtime on a battery charge. This may sound like a severe problem for things like the Pinephone which are already plagued by short runtimes, but the Pinephone is not the main problem in my mind (since it already has a smart PMIC) - the main problem is the Pinebook Pro, whose battery runtime is enormous and whose battery charge limits cannot be changed without an involved hardware mod. And perhaps also the Pinenote; I don't know if it's going to have a smart PMIC, but with an e-ink display, it will almost certainly have plenty of runtime to spare as well. The tradeoffs I'm talking about here are considerable - it's not just an 8-year vs. 10-year lifespan difference, it's more like 3-year vs. 10-year, and I'm really not exaggerating that. This is based on real, repeated experiences that I have had with my own devices, which have been starkly dependent on my own treatment of their batteries.

I definitely do not understand the relevance of electric cars and power grid load leveling here. No one is suggesting that someone else should be allowed to use your Pinebook Pro's battery to buffer someone else's power demand, and I want to emphasize that I am not proposing any mechanism that would ever result in your devices being nearly-discharged after being connected to a working charger for a long period of time.