In the early days when we had little field experience we recommended connecting the alternator
to the house battery and letting the Combiner top off the starting battery. However after 20 years of experience it turns out to make no difference and leaving the alternator
on the starting battery maintains warranty on new engines.
A Combiner that can carry the full output of a 100amp alternator will always charge an auxiliary faster than an echo charge limited to 15 amps.
True, a regulator
with an external sense will detect the battery voltage instead of the alternator voltage and avoid the 0.7 volt drop. BUT WHICH BATTERY DO YOU CONNECT THE SENSE WIRE TO? If it is on the bigger battery that comes up to voltage slower, won't that overcharge a smaller battery? If you connect it to the starting battery and it comes up rapidly won't that leave the house battery less than fully charged? It also can be catastrophic if you have battery switches, I've seen and heard of batteries getting fried when the sense wire was on a battery NOT on charge so full output went to another battery bank.