Seems like you want the charger to be aware of the hosts state of charge. Typically telemetry only flows from device to computer, which this violates.
Most laptops/tablets/phones/&c do know their state of charge & can in software disable charging, although only some expose this to users. This is often available in Linux but I dont think any particular scripts/apps for controlling this have risen to notice yet.
But you are still asking for a complete rewrite of how everythinf works, for it all to be totally different. It's not a totally unreasonable ask, it's just not in reach. Unlike my discussion above, which proposes a plan entirely doable with standards we have.
USB-PD negotiates power delivery, but it doesnt communicate battery or other status. It uses a different sideband to nevotiate outside regular usb communications, and conveys very limited information. There's no battery informatuon conveyed.
My above post spoke to how multi-decade old USB HID standards can be used to present current battery status for battery packs. We'd have to flip the relationship around- make the charger be a host that can manage an attached battery, the laptop be a peripheral that exports it's power status, to invert tbe control system as you want, to make the charger responsible for battery managememt & not the device. Or we'd need to radically revamp usb-pd & layer in a lot more capabilities.
It'd be cool, in some ways. Plug in any device & it'll only 85% charge. But it's also far more complicated & rewrites all the rules in every way, unlike what I was talking about, which is just battery packs & chargers kind enough to export their status over some very very old simple specs.
Yes I agree that my wish is unreasonable and your plan is much more attainable.
I don’t want to flip everything on it’s head (OK that’s a lie: I would love to flip almost everything in the name of having better solutions). But what I mean to say is I know what I’m asking for is unreasonable and certainly unrealistic in a 1-3 year timespan, but I know it’s possible and I like to dream because sometimes moonshots actually land you on the moon
Most laptops/tablets/phones/&c do know their state of charge & can in software disable charging, although only some expose this to users. This is often available in Linux but I dont think any particular scripts/apps for controlling this have risen to notice yet.