Here is the manual for a Magnum Energy RC like the one in my RV. http://www.magnum-dimensions.com/sit...ev-D-ME-RC.pdf
Starting on page 27 is the fault codes.
I recently had an issue where the main fuse that goes from the inverter to the positive side of the battery bank blew. If you have a multi-meter you can check for voltage on both sides of that fuse. If you have 13+ volts on the charger side and less on the battery side you have a blown fuse. Of course you can also just check for continuity across the fuse.
Keep in mind this is a LARGE fuse. Mine was a 300A bolt in fuse.