Good Morning Alan,
At the risk of sounding stupid, what do you mean by "low SOC batteries?"
I avoid letting my battery voltage drop below 24volts. They are standard lead acid.
I was also looking into a means to shut off the alternator from charging. Is your last sentence a description of that?
Overcharging on extended periods of motoring has presented problems, and if I could have the option of shutting off the charging circuit from the alternator to the batteries, it would be fail safe for the battery bank.
Spirit Amel 54 #14