"I explained that the battery cables came right from the converter and the current doesn't pass through those breakers to charge the battery. He says I'm wrong. AM I??"
Simple test. Unhook the breakers and do another voltage measurement. You don't do this to say who is right. You do it for the knowledge to fix these things in the future.
Your post doesn't really say he was angry at you for helping. The problem is fixed and he didn't pay an RV shop $150 an hour to troubleshoot and replace parts until they guessed right.