The display is only indicative and not very accurate.
First, I would change the display over to the battery one and see if there is a current drain, or the batteries may be just a little flat.
Start the engine and see if the 'Gen' symbol comes on, it takes a mo for the display to change so don't panic initially. If so, all would seem OK and you just need to plug in the van to the mains for 12 hours or more to charge the batteries up fully.
Then see if the situation is the same, once they have been charged.
Alan