To the original poster..
Technically what I am about to describe is a "Failure of the converter" but.. Well fixing it is a bit easier than you are fearful of.
Most converters have one or two (or more) fuses, these are usually 30 amp, and are often in parallel. They are called "Reverse Polarity" fuses.
SOME converters, if you OPPS your battery, can put out enough current to pop these fuses.
HOW to fix.
Step one, Pre-charge the house batteries using an external automotive type chargber.
2 UNPLUG from shore power (or shut off breaker to converter)
3 Replace the fuses, all of 'em, inspect them as well if they look blown you are likely on the right track, but even if they do not look blown.. Replace 'em.
Hook digital voltmeter to battery and note reading
Plug in (Reset breaker to ON).
Readiong should increase, likely by over a volt though it may only go up a little at first.