Thank you all, so much!
Mex: Yes, I spent $200 on that chassis battery. At that price, I expect perfection! (I would have bought cheaper, but my memory problems + the fact that I am used to AGM caused me to kill several cheap wet batteries. I can't keep track of the differences.)
Is your first post ("Discharge reluctant battery to 12.2 volts") referring to the house battery that overheated? You said that was a fail, but then you go on with instructions for discharging and recharging. So I'm not sure if you're talking about the same battery there, or if you are talking about the chassis. Clarification, please?
BFL13: The chassis voltage readings are at rest. Not sure of your question, but no, it wasn't ever above 13 after resting from the charging. That was with a meanwell at 14.55v.
And no, I didn't do the 40 amp load test on the chassis battery. The first time, I started the engine four times, and then hooked up 12 amps (two incandescent lights). The second time, I used the lights for the whole thing. That was before I busted my space heaters out of storage for test loads :-)
Good point about loose terminals being a possible reason for the heat on battery A. The terminals were tight, but I forgot to mention that the cable ends were a bit corroded. I sandpapered them, but maybe not enough. And maybe the fact that it was the first battery I used them on is significant. I could retry.
Sadly, I did not think to check the temperature of battery B when it was being excessively charged. I can't really tell you if it got hot. I'm kicking myself now, that I didn't do that.
2oldman: An AGM should be above 13 when fully charged, and should hold its charge for months when not connected to anything. I was maaaaybe gonna settle for the 12.93, but not if it can't hold steady at that voltage.
