If batteries get commoditized then it could be an easy process to replace the battery. It becomes no different than many other repairs you would typically make to make a used car sellable.
However it will likely require legislation to ensure there's no DRM bullshit in the battery packs.
It becomes an issue because batteries are so much more expensive than other things you can get though. It's not replacing a alternator, it's replacing a $15000 battery "set". Also I'm hoping electric car longevity will prove out the value in this. Electric car drive trains "in principle" should have much longer lives than gas engines.
However it will likely require legislation to ensure there's no DRM bullshit in the battery packs.