First: are the batteries Maintenance free or what we call "Flooded wet cells"?
How to tell the difference, Flooded wet cells you can remove caps and add DISTILLED water.
If Flooded did you add Distilled Water? If so how full.. Some folks fill 'em right up.. Some (like me) believe that 1/8 to 1/4" below the bottom of the filler tube is a better "Full" line.. And being as when I was trained Maintenance Free 12 volt batteries were few and very far between.. I trust my training. (Heck when I was trained Six Volt Batteries, always flooded, were still common in cars)
If you over fill, it will spit acid out at you. (oh yes that wet may be acidic, wash it down good)
Now: Somewhere in your rv is a device called a CONVERTER.
This is a box. May be part of something else (Read on) it will have a fan, 120 volt wires and 12 volt wires, Other than A/C the only thing that meats that description.
Now in MY RV, I have 3 devices.. one is a 120 volt power distribution panel (All circuit breakers, NO fuses) one is a 12 volt panel, (All fuses and LED's no breakers, though some are now being made with breakers)
And a stand alone converter (Box described above).
Many have an intergrated panel.. Both 120 volt breaker, 12 volt fuses behind a common door.. May be marked WFCO, or Parrallex, or Magnatek or ______ (other names) but you open this one door and both fuses and breakers appear
The converter is often part of this assembly as well
Why am I telling you all this about converters? The make and model please.. if part of distribution panel, you will likely find this information on the inside of the DOOR I just described.