Data is always good.
Even if the voltage regulation of the alternator is not ideal or even half way there, a long length of 10AWG to house bank is not doing the depleted battery any favors, especially if it is coming off the engine battery instead of the alternator(+) output stud.
I do not know how difficult it is to change an internally regulated alternator to an Exernally regulated one, and what ever vehicle considerations there are regarding engine computers, BUt I have been controlling my alternator with an external regulator for two years now. The wires which go between my engine computer and the original field terminals on the alternator, have a 50 watt 10 OHm resistor tricking the engine computer into thinking it is still hooked to the alternator.
Getting 14.7v at the depleted house battery terminals anytime the engine is running, is as good as it gets. Watching how many amps flow at 13.6 vs 14.7 reaching battery terminals, is about 2/3rds greater amp flow at 14.7v, at least on my battery.
So if your vehicle voltage regulator says 13.6v is just fine and dandy, your are kind of screwed.
If one has to do the big inverter on engine battery powering their converter to get that14.4+ volts at the house battery terminals, so be it, but wiring up a big inverter outside the engine compartment with thick copper, running the AC wiring to the converter, and the other considerations, well thick copper and better voltage regulation might not be any more overall work or cost of the sterling DC to DC converters, or the Ctek smartpass and likely a few other similar products.
The inverter powering converter to charge house battery could simply be depleting the engine battery too, and likely will be, at idle. The double conversion seems so wasteful.
