Nuclear wars would mostly involve thermonuclear weapons detonating high enough up that their neutron flux will essentially dissipate before reaching the ground

Nuclear wars would mostly involve thermonuclear weapons detonating high enough up that their neutron flux will essentially dissipate before reaching the ground where all the cars are. That will maximize the area destroyed by the shock wave. It's true that a neutron bomb used tactically against ground targets could transmute car batteries. But those would tend to be used in the countryside against armor formation rolling through rather than against cities where all the cars are. And they have a fairly small radius of effect anyways. EDIT: And in any event, I'm sure that the transmuted cobalt will be the least of our problems if it ever becomes relevant.