Given the huge environmental cost involved in manufacturing a car, 20 years seems fair.

I’m still driving a 26-year old Nissan Micra – though it’s now on its last legs: the Irish climate isn’t kind to steel and we’ve had to have the under-carriage re-welded three times in the past five years. :(

EV batteries are expected to offer about 60-70% of capacity at 20 years. I think that's really good compared to general wear and tear of the car.

But let's go back to the original point, about being able to UPGRADE (not repair/replace) battery in the car. 20 years old car is worth like $1k-2k, which is fraction of the cost of the new battery.

While it's cool thing to do for hobbyists, it makes 0 economical sense.