RE: Proper charging voltage
I've seen another and different setup.  An '87 with a stock starting battery
and two Yellow Tops in parallel, connected by a Shurepower isolator, not
separator. That specific isolator is sending 14.2+ volts to the batteries.
I understand that is not normal but that is the measured output.  The Optima
(AGM) batteries seem to like that setup, he has all kinds of power to spare
and the aux battery pair, after a couple of hours drive, are up to the 14.2
V or so that they like.  And this setup, with the original batteries, has
been running like that for seven years or better now.  BTW, the starting
battery get's checked for water level on a regular basis, no excessive
boiloff or evaporation.
I've considered going to an adjustable regulator and setting it at about
14.2 V so that my AGM aux battery gets to charge it likes while driving.