I'm confused. The battery isolator/combiner solenoid is suppose to disconnect the batteries from one another, if the voltage of the one battery hits a low threshold and the other battery is not at a voltage high enough to be a charge voltage. That threshold should be about 10 volts. There are several configurations. Fundamentally, when the charger is supplying charge voltage, somewhere around 13.5V or more, the solenoid combiners the batteries so they are all charged. When the charger is off or not working, the battery's voltage is somewhere near 12.8V. For some solenoids, at this voltage or less, the solenoid is in combined operation until either battery bank drops to some low level, maybe 10V. For other solenoids, the absence of charge voltage will disconnect the battery banks from each other.
Gil
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