Two things provide 12VDC power to your Power Distribution center where all the 12VDC fuses are located.
The Battery and the Converter/Charger unit.
The converter/charger unit has to have 120VAC to operate and there should be a 120VAC circuit breaker in the power distribution panel just for the converter unit. Would be a good place to check to see if the 120VAC breaker has been tripped.
You can check the BATTERY OUTPUT of the converter/charge using an inexpensive digital multimeter ($7-$20) form Lowes-Walmart-Amazon-or any number of autoparts stores. Your converter.charger should read 13.6VDC on the cables feeding the distibution cable and the battery terminals.
You could have a bad converter/charger.
You could have also installed the battery cables wrong on the battery terminals. This will blow three fuses between the battery terminal and the Power Distribution Center. Two fuses are located on the Power dist unit marked "REV POLARITY" or something like that (These two fuses are usually sitting off by themself). Another "IN-LINE" fuse in the positive battery terminal lead located close to the battery may also be blown.
The best way to determine if the battery cables have been reversed is to look at the battery case and fined the "NEG" or "-" symbols stamped on the case. The battery cable connected to this NEGATIVE terminal should always go to the trailer frame ground connection which will be real close to the installed battery. I have this in mind everytime I grab a battery cable as they ares so easy to get on the wrong terminal. Once you have them on the correct terminal some folks will pick up some of those cable markers from the autoparts stores aand label the two cables POSITIVE and NEGATIVE so that they will all know which is which. RED fingernail polish on the POSITIVE battery cable works pretty well also. You cant reply on the installed wiring colors as the different from trailer to trailer.
In the automotive world RED is POSITIVE and BLACK in frame ground.
In the Trailer World BLACK is POSITIVE and White is frame ground.
The BLACK CABLE will eat your lunch everytime as the two worlds get mixed together when it comes to batteries....
This is why i just hand trace out the cable that is connected to the NEGATIVE marked termial and make sure it is the one going to frame ground.
Your problem sounds more like a bad converter to me since the ceiling works with just the battery connected.
Roy and Carolyn
I claim Horse Creek Country in Southern Ill - Momabear is from North Texas
We live in King George VA
RETIRED DOD DOAF DON CONTRACTOR Electronics Tech 42YRS
"We're burning daylight" - John Wayne
2008 STARCRAFT 14RT OFF-ROAD POPUP with PD9260C and three 85AH 12VDC batteries
2010 F150 FX4 5.4 GAS with 3.73 gears - Super Cab - Towing Package - 2KW Honda EU2000i Gen
K9PHT (since 1957) 146.52Mhz
"We always have a PLAN B"