I had similar issues when I bought it home from storage. Spent days resetting brakers, cleaning battery posts, converter would not even come on to charge batteries, only 1.2 volts showing on multimeter.
Called a RV tech and he said when the batteries get that low the converter will not charge them. I removed them from the coach charged them back to 13V, took 2 days, they put them back in and all has been fine since. Converter heeps them at 13.3V, slide and awning now work. Also note the batteries only charge when the disconnect switch is on use.