It turns out that Marinco Guest website has some good diagrams. In addition to that I found some technical documents about smart charging in general.
Although my research was fairly brief, I learned a few things I wasn't aware of, the most important being that multi port smart charges come in two designs; a single common DC ground and individual grounds for each port of course in addition to the individual positive connections.
If your charger has two leads for each port in can also have separate microprocessors for each port. If the charger has a common ground ( for example, a 2 port charger has three output wires) it can not have separate microprocessors.
Separate processors allow a charger to work with different type of batteries at the same time.
The other important detail to insure is that for a multi port individual ground charger, the positive and negative charge leads should be connected to the same battery. The negative and positive wires of a specific port should never be attached to different batteries. That means that the posted diagram for suggested connections for two batteries could be harmful to the batteries or the charger if the charge ports have individual grounds.
The Marinco/Guest manual has diagrams of several different battery configurations.
It is correct that the pos/neg pairs of charger wires should go to "the same battery". My diagram shows 2 batteries in parallel using one charger bank pair . Essentially, we are trying to trick the charger into seeing "one" larger battery by connecting the charger across the "one" battery. I will concede that Marinco/Guest never tell you that you can do that. They will have you connect a pos/neg pair to each separate battery. The old Guest used to give diagrams like that for parallel configs(and various series configs). Marinco seems to shy away from endorsing parallel configs altogether because having only one physical battery per charger pair eliminates a lot of variables that they have no control over...(like long unbalanced wires between parallel batteries