Car power packs are batteries in the other sense of the word. They can be disassembled and culled. So what matters is the health of the best 1/kth cells in the array not the overall array health.

I think you may be confusing worn-out batteries with damaged batteries, these two subclasses do not have the same properties

Except that the cigarrette is only 30% smoked and still perfectly fine to smoke for a while longer (if you insist on an analogy).

Car battery packs are really good; even the oldest Teslas are only now getting to less than 80% capacity. They are designed not to swell/fail if they're worn, else there would be a lot more car fires.