The convert/charger should be putting out 13.6VDC or what other smart mode it may be in when connected to shore power or running off of generator and you should be able to see this DC Voltage at the battery terminals...
If you just installed the battery this raises a ref flag as you may have the battery leads reversed... The best to tell is look on the battery case and find the symbol '-' or the word 'NEG' and make sure this is the terminal being connected to FRAME GROUND close to the battery. It could be a WHITE wire which is common for RV Trailers...
Using a multimeter at the battery terminals you should read 12.6-7VDC if the battery is fully charged. The when you apply shore power or hook up to the generator this battery DC Voltage should jump up to 13.6VDC or what ever DC VOltage the converter/charger is doing at the the time.
If you indeed had it connected in REVESE ORDER you may have an IN-LINE Fuse blown or in-line circuit breaker tripped close to the battery. There is also two fuses near the converter/charger unit that is called the REVERSE POLARITY fuses that also may be blown...
Also note that the trailer ceiling lamps should be working ON/OFF if all of the connections/fuses are good from the Power Distribution Panel where the converter/charger is usually located when NOT on Shore Power or generator. Those lights work from 12VDC source... If any of the fuses have been blown feeding the battery terminal than this will not work.
Most likely you may have sparked the battery terminals or connected the battery cables to the wrong position when you hooked it up. I have my battery terminals marked with RED FINGERNAIL polish to identify POSITIVE cables... ALot of folks take a picture of the connections with their cellphone and can easily go to the picture when working around the cables.
NO HARM should have been done to anything if this has happened... That is why the in-line fuses are there for protection... In the RV WORLD the wiring colors are BLACK for positive and WHITE for frame ground. In the Automotive world the battery leads are RED for positive and BLACK for frame ground so you can see how easy this gets switched around.
with your battery DC Voltage at that very low DC OUTPUT is really bad for the battery cores inside and hopefully you can get the DC VOLTAGE up to something over 12.0VDC to keep internal damage from happening inside the battery. It may already be damaged and will have to be replaced with a new one... If i fin one this low is telling me I may have a bad cell inside the battery and usually try to bring the battery back to life using an outside battery charger.
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS