On the surface it might sound nuts but is it?
Many people's experience of rechargable batteries... especially lithium batteries... are those in laptops and phones. Those batteries have a nasty habit of expiring after a year or two of use. So is it not perfectly reasonable, when they hear that EVs has lithium batteries, to make the assumption, albeit incorrect, that the car batteries might last the same?
I am not at all surprised at the question. It seems a reasonable question to ask IMO.
My answer is that EV lithium batteries, although based on lithium, are quite different in their chemistry and do not suffer from the same short lifespan. I also say that the battery technology has been thoroughly tested and ask if they think that the car companies would risk car batteries dying in a few years? They would be the laughing stock of the car world. This seems to satisfy most people.