Battery Charging Problem ***UPDATE***

DrewE wrote:

pianotuna wrote:

LOG wrote:
Lets say a new motorhome with a smart charging system also included a battery combiner that connected the chassis battery and the house bank when the engine is running.
Would the ECM still see the chassis battery as fully charged and drop the alternator voltage before both are fully charged?

Yes the ECM "sees" the chassis battery and drops the alternator voltage.

Yes and no. The ECM sees the voltage at the chassis battery. Provided the two batteries are connected with a low enough resistance connection, the voltage will be practically the same at both batteries, and the ECM will see that same voltage and not deem the battery to be charged and drop the voltage until both are at whatever it thinks is fully charged.

Not all motorhomes have a connection between them with a low enough resistance for this to work too well. That could be because the wire is insufficiently heavy, or there's a poor connection somewhere, or in some cases because an auto-resetting circuit breaker is clicking on and off (and, of course, has a very high resistance in the off state). The greater the resistance is in the connection, the greater the voltage drop will be to the house batteries, and the more prematurely the charge voltage will drop.

Thanks for that explanation. That makes sense to me.
However, my understanding is that we are talking here about a "smart" charging system on newer motorhomes that come from the factory with a system deigned to do that.