battery charged at 12.7 V, not getting power to the RV??

I went through this this spring. Here is my link and problem solved

Bad 50amp breaker no lights on battery

Just went through this. Ours was the converter. $200 and we were back up and running. The telling tale was the 110 outlets worked when on shore power, none of the 12v appliances worked.

Does sound like a corroded or loose battery terminal connection or (as already stated) a loose ground wire on the main terminal block.

Might be a bad cell in the battery if the battery is only charging fully to 12.7
13.2 should be a full charge.

Pop the fill caps off the battery and look at those water levels.

On my last travel trailer there was an inline fuse on the positive battery turminal lead.Do you have one and could it be blown? Just a thought from my experience.Otherwise like already stated you need to consider the converter.Disreguard ,I reread your post ,cant be a blown fuse if you are getting power in certain instances.

Lots of questions. First of all, were you plugged into shore power (commercial power)? How old is the RV and what brand and model? Does any of the other 12v equipment work? Such as the vent fans. When you turn on the second light and everything quits, does this include other 12v equipment? Sounds like the converter/charger is bad but without further information, that is a guess. First of all I would check the ground wires to the trailer frame and to the converter where ever it is.