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.

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

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.