Mike, when you are here, look at my Link20 meter. It is very good for this kind of thing.

The LaMarche, which is an old ferroresonant charger if I am not mistaken, does not charge very efficiently. The charger in the inverter is almost certain to be a HFO type charger and much more efficient, with a flexible charging profile. If it can switch for different kinds of batteries, I would bet that it is.

What you might think about is adding better regulators to the alternators- external regulators that are programmable. They make the alternators much more efficient and will control them to shape a charging curve that is like the one a modern HFO charger puts out. I did this and (after my mysteriously blown alternator was repaired) I like the way the system performs. I had no problems with dead batteries with this system with the prior engines.

The best way to set up a boat's DC systems is to have both engines start from one bank of dedicated starting batteries and the house loads on a dedicated bank also. One engine charges the starting batteries, the other charges the house bank. They can be paralleled if need be, and there is an echo charger or combiner to keep them both charged if only one engine is running. This system is not that difficult to set up and it really does work better for all uses.