When ever we plug in to our house/garage 120VAC receptacle we always test our DC voltage at the battery terminals to make sure they are being charged.
A typical charged up battery will read around 12.6-7VDC when fully charged and SHORE POWER NOT turned on.
When you connect SHORE POWER the DC VOLTAGE at the BATTERY should jump up to 13.6VDC indicating the on-board CONVERTER/CHARGER is being powered up and the battery is connected to it.
You may have a blown fuse or battery disconnect between the converter and battery terminal. Just plugging-in is half the game for us...
If you find blown fuse then you may have hooked up the battery in REVERSE ORDER.
Roy Ken