"i let the pm rest about 5 minutes, then did a bench test with no load… it quickly rose to 15.2v., and dropped to 14.15 at the 15 minute mark. so i connected it to the other 215 bank, which were at 12.76v, and it quickly rose to 15.13v, and then 15.18 over a couple more minutes.
... it was late, i was tired and hungry, and perhaps a little tipsy by this point, so i shut ‘er down for the night."
You almost had it and turned back!!! Drat. OK it seems there is something wrong with the R of the first pair but the second pair might be ok and provide "normal" results. Maybe.
Please do it all again using that second pair. You want to see that 15.13ish last past the 15 min for a good while, then all being well, reduce your Vabs (as now thought to be) so your "boost" (as now thought to be) is 14.8 instead of 15.13ish. Maybe then it will do 14.8 till amps taper and stay at 14.8. Never know until you keep at it.
What is different about the first pair from the second pair is a question that must be answered. More detective work!
