That #6 might not be the only culprit. There is still the possibility of loose connections on the positive path and additional R somewhere on the neg path, ASSuming there is nothing wrong with the PM75.
EDIT--also the 120v input has to be good or it won't run right.
Don't forget that you might get that 15 min of 14.6 voltage at first but at what amps? With low batts (under about 75% SOC) you should get some time at 75a.
Purest test of the PM itself would be from it to a pair of low batts using a short fat set of wires, well connected. Be a PITA to arrange that when it is now all installed.
