I had a converter go bad.
I was on 120v and first noticed that the lights were very bright. Then I smelled something strange around the battery box, it was discharging gas. I pulled the 120v power plug, disconnected the battery via my switch, then disconnected the battery. I then plugged back in the 120v and checked the voltage of the RV from the 12v outlet (cigarette lighter) and it registered 24v.
It was indeed that the converter had failed, and was putting out 24v. Luckily I had caught it in time before any damage was done, including to the battery.
On your meter, maybe check it on another battery, and see what happens? If the rv battery had failed, your charger would be registering high amps and wouldnt come down, and the battery would start boiling inside. Was anything strange going on when charging?