Use the same troubleshooting method as
No DC power. Shore power good.
Take a multimeter. On shore power, check each post of your red 50A self resetting circuit breakers near your batteries. They should all read the same (about 12.4vdc).
Now remove shore power. Check them again.
Which ever one is NOT showing 12vdc on the post, it is bad. Replace it.
If they all show the same, take the battery to an auto parts store and have them test it.
There is also a procedure to test your converter output.
Progressive Dynamics troubleshooting and manuals
https://www.progressivedyn.com/servi...er-converters/
https://www.progressivedyn.com/suppo...hooting-guides
I attached a PD converter troubleshooting file and uploaded it to the files section at the top of the webpage.
Hope this helps