I first ran into a WF8945 Converter/Charger back in 2008. Everyone then said it has to be closer to the battery... I finally rigged up with a large fat cable just sixes away from the battery terminals with same results.
Then I ran down by battery to around 10VDC and hooked up to it again with the short DC cables and it jumped into bulk mode and stayed there for a whole 46 seconds and jumped back out to 13.6VDC.
That's when I gave up on it haha...
One guy on the RV NET back then had figured out how to rewire the mother board to make it work.
Got me a PD9260C 60AMP converter/charger then. It goes to 14.4VDC first time you turn it on.
I still have mine in the circuit but it is unplugged from 120VAC. If I ever need it I can just turn it on and it will give 13.6VDC at 60AMPS haha... Thats almost a good PLAN-B I guess...
Roy Ken