Unless your old batteries test bad under load, I'd suspect a short or some item drawing too much current during the night. Appliance controls and alarms draw some 12 volt dc current from house batteries
If you disconnect the positive or negative cable on the house battery and connect an ammeter to the cable and battery post you may see how many amps are still being drawn with everything apparently shut off. If you are not able to test, have it tested by a trusted RV repair.
Was there a light left on in your storage compartment?
Did you have the furnace or furnace blower or ceiling fan running overnight?