First things first - Is there a battery charger in the system? Some SMB builds I have seen with shore power do not have a charger. The shore power is connected to the main panel and the in-cabin plugs are connected to that panel. If the main panel has a charger or converter label on one of the plugs then there should be (or was) a charger included in the build.
An inverter can be present w/o a charging feature. All it does is provide 120v to the 120VAC receptacles when on by inverting 12 vdc from the battery to 120vac supplied to the cabin plugs.
You may find a Battery Wizard or a converter near the house battery location. These would be SMB types of chargers they installed.
Do you have an inverter? Type / model#?
The 4D Battery mounted passenger side frame, behind the differential, or ?!
A picture of the battery installation area, fuse panel, Shore power main switch panel could help us get you connected.
Jeff, feel free to call me, too .