They could build them in small packs like swappable batteries in scooters. Then when there's bad individual cells you can unbolt that smaller pack and either get it replaced or pull it open and find the bad cell.

Unfortunately, they are already engineering ICE vehicles to be so convoluted and tightly packed that a common wear item like a battery needs an hour removing shit that's in the way. They are trying to force you to go to the dealer to get it done. I think it was a Chevy truck that had the battery tucked partially under the intake and some plastic moulding under the windshield.