That said, it's probably a UX problem. Once EVs stop competing on range so much, it'll make sense to just designate the last 10% of battery as "reserve" and not count it in the battery level indicator.
Arguably it should be far easier to get those economic incentives aligned as chargers are far simpler mechanically (they are just plug sockets with weird over-engineered male adapters) and most of what breaks on them is either vandalism or a small subset of existing problems of gas pumps: credit card reader malfunctions, display/screen problems, internet connectivity issues for account management/credit card transactions. (All the human UX points of contact.)
> Once EVs stop competing on range so much, it'll make sense to just designate the last 10% of battery as "reserve" and not count it in the battery level indicator.
Most already do (even while still competing for range) because it's a battery maintenance requirement. Li-Ion cells generally don't like being 100% full, especially not for long periods of time, and sometimes have a preferred "directionality" (ie, a cell should only be charging until it hits 100% and then you can draw from it and vice versa once you start drawing from the cell you should keep doing so until it hits 0%) so battery controllers already have to do a bunch of math to keep a "reserve" so that they don't violate "directionality" (you always want cells in the "charging" direction available even while driving for regenerative braking storage, for instance) and don't generally hit 100% charge for long rest periods, but instead 95% or so.
> it'll make sense to just designate the last 10% of battery as "reserve" and not count it in the battery level indicator.
Very questionable? Why would you do that?
We don't do that for gas cars either.
I once, embarrassingly, found myself on the highway with an empty tank of gas and 20 miles to the next gas station. I watched the estimated miles remaining indicator tick down mile after mile, ticking precisely my passage. At 3 miles estimated remaining, I pulled over because there was a very wide safe shoulder, and I didn't want to putter out in a less-safe spot.
I don't want to try the experiment of letting it tick down to zero and seeing if I still have 10 miles or so left.
I think the use cases for field-swapping a (part of the) battery pack are the same as for carrying extra fuel canisters with you, which I can only speculate about, because I've never been in such situation with an ICE car.