Hi a "fully charged" wet cell battery is about 12.6 volts unloaded (no loads and not charging). When charging a wet cell battery normally you should see at least 13.1 volts or higher with your voltmeter across the batteries.
Sounds like your coach batteries are almost back.....you should be able to disconnect the car charger and disconnect the shore power and try to operate the latch relay with your use store switch. If it closes properly you should have DC lights and DC coach power now. If you don't hear the latch relay operate then you have a problem. If the latch relay closes and you don't have any DC lights of fans then you may need to find where the 50 amp resettable breaker (typical) is located and reset that. If DC coach loads start working normally then plug into shore power and check the coach battery voltage to make sure the voltage is now 13.1 or higher.
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