Boiled one of two 5th-wheel batteries

Batteries have been replace and thus far, all is well. I was able to contact the converter manufacture too, and they sent me some testing instruction. Thinking back to the three weeks of charging I did before the morning of the event I recall seeing about 12.5volts at the post, and although this registered with me as normal, I know a fully charged battery will reflect 13 to 13.5, not 12.5. Best guess at this point is; I just had a bad cell or bad battery. Time and trial will tell. Battery replacement was free, as I had purchased them from Costco, and following my honest tell of sorrow and woe, they said that they had observed some returns on bad batteries this season. The didn't bat an eye about it and this made my day. I have also added a battery hydrometer to my collection of battery tools and I will now start checking each cell as part of my battery maintenance.
I thank everyone for the quality response to my meltdown (pun indented) and I will update this post should something change.

For now I will end this story with a two thumbs, a smile, and an oldie but goodie, live long and prosper.

Traveler1960