I work in the industry and from what I see the "bad" batteries are usually manufacturing problems and they stop working very early in their lifecycle. The degr

I work in the industry and from what I see the "bad" batteries are usually manufacturing problems and they stop working very early in their lifecycle. The degradation of charge capacity though is almost always completely dependent on usage patterns though, if you trickle-charge instead of fast-charge, don't do a lot of full cycles (100% to empty) and keep them in reasonable temperatures they will lose very little charge capacity. BMS systems in cars have been getting better and regulating the temperature of the batteries even when the car is off though. Unfortunately the used market doesn't have a reasonable way to measure charge capacity, the only way out is for regulations to force disclosure of current charge capacity and total power cycled through the battery and tools to get that information out. Those two metrics would provide similar information compared to mileage for a gas-powered car. Also if I had the capital, space and know-how I would be buying every single dirty-cheap used EV I could get my hands on and store the batteries. Soon those batteries are going to be a gold mine for recycling. Recycling li-ion batteries is like aluminium recycling, very energy intensive but you get almost all the raw materials back and recycled aluminium is cheaper than newly mined aluminium. Soon you will see people shipping those used batteries to places with cheap energy for recycling (like Iceland for aluminium recycling). The process is more complicated than aluminium and there aren't that many spent batteries around which is why this is not a big thing yet.