Since you mentioned taking out your batteries, if when reinstalling them, if you hook the cables up backwards (even for an instance), you will blow the reverse polarity fuse(s) for the converter.
The converter will not function until these fuse[s] are replaced.
Depending on what brand you have, depends on where they are.
In this pic, you can see the 40 amp reverse polarity fuses separate from the other ones, and below where it states they are reverse polarity fuses.
You might want to check that out and make sure your fuses are good.