Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 10, 2025 ...

Dean,

The .7 VDC or so loss across the diode-based isolator is ONLY important from a theoretical efficency standpoint (you are burning diesel to work the alternator a little harder to turn part of that extra work into heat that is dissipated by the fins of the isolator).

Since the alternator sense wire is on the BATTERY SIDE of the isolator, the batteries are getting exactly the voltage you prescribe.  Yes, the voltage on the alternator side of the isolator is higher, but no battery manufacturer should have any interest in anything but the voltage AT THE BATTERY.

BTW, both manual switches and solenoid-based isolators have zero voltage drop across them.  There are a lot of coaches with solenoid-based isolators with the "both" signal coming from an ignition hot source.  BIRD relays are a more sophisticated example of solenoid-based isolators.

Dean,

Yes, if you are running a high amp draw on the house battery such as the furnace(s),  you could leave the switch to ON.  Depends on how long and how many amps.  If the batteries can handle the draw, let the CG's electricity recharge them that night (but, would not run them down below 50% doing that).

Dean
I second Brett's response.
 
With your dual 8D capacity, routine use of  low-current appliances (computers, dc control boards, parasitic loads) going down the road, are not going to change your house battery bank SOC (State of Charge)  rapidly. 
If you use resistance heating devices (like a toaster, a clothes iron, AC heat strips, infra red heater) or microwaves, or motors (residential refer, furnace blower(s), exhaust fan(s), CPAP machines with humidity heaters) types of loads, then the SOC rate of change will become apparent. 
With reasonable care, you should easily go 8 to 10 hours of driving time without needing to start the generator (preferable to charging the Lifelines at something greater than 14.3 Vdc) or closing the manual battery isolator switch to charge the house bank via the alternator.

Sidenote:
It's an interesting dilemna to have an engineer contradict his own company's technical literature.  Especially when that engineer also thinks that a 0.5 to 0.9 Vdc voltage drop in a power diode is unusual and doubly so if the engineer doesn't understand that the most commonly used, most reliable, battery isolation devices are properly sized diode isolators and properly sized switches.  As Brett says, he should only be concerned about what the voltage is....AT your positive battery terminals. 
Also, his statement about an alternator output voltage value of 14.7 Vdc overburdening the alternator begs question.  An alternator's output voltage doesn't have much to do with an alternator's load.  It's the amount of current that is being generated by the alternator that matters in terms of alternator load, wear and tear. 

Anyway, best wishes, Dean and no.  No test in the morning.
Neal

How much dry camping you do (followed by having the alternator charge the house battery)

The On-Off switch also allows easy charging of the chassis battery from your inverter/charger unless you have made other arrangements for charging the chassis battery.