"If they were smart, they…
"If they were smart, they charged him for the new battery plus labor and ate the rest."
I think If the dealership was smart, they would have tacked 30% on to the master mechanic's invoice, in addition to their own diagnostic fees, plus the battery, and passed it along to the truck owner.
Why would anyone expect a free repair when it was obviously beyond most mechanic's abilities to troubleshoot, let alone the truck owner's ability.
Let him send the bill to the windshield repair company and hash it out with them.