Davydd makes sense. If you are not in a hurry to move the van, I would buy a trickle charger and use it to charge the engine battery until you can start it. That way, the next time you don't plan to drive it for a while, you can leave the trickle charger on the engine battery. You should have a disconnect switch for the house battery, it should be switched off whenever you aren't using the RV. 120 V household current will charge the house battery. I wouldn't replace the batteries until they fail a test. Good luck with your predicament, let us know how you make out.