It would help if we knew just what model you have - there are a lot of Fleetwoods. Your description of the batteries is a little confusing to me. Typically you will have two groupings of batteries. One will be a 12 vdc battery to start the engine and run chassis systems, the second would be your house batteries to run the house portion of the RV. Typically they will be 6vdc golf cart batteries hooked up to simulate 12vdc and there are 2 or 4 each (but some house batteries are 12vdc).
If you have a residential refrig as it sounds like, you have an inverter that takes the dc voltage from the house batteries and converts it to 120 vac to power the residential refrig. Depending on how many house batteries you have it can run the the residential refrig for 24-36 hours typically. To maximize the time the inverter does not run all the 120 vac outlets but may run the TV outlets also.
I am sure others will jump in and expand my basic info and elaborate further on it.
I further suggest you go to the Fleetwood website and find Customer Relations and ask for a manual for the specific coach you have. My experience with them has been very good but not so with the actual manuals. Fleetwood manuals are generally not very comprehensive or helpful, I have had RVs for many years but I would hate to be a new RVer with the manuals that came with our new Bounder.
Hope this helps some. Good luck.