Abstract: First and second batteries each connected in parallel with a load and a battery isolator connected between the first battery and the second battery and the load including a series pass transistor connected in series with the first battery and the load and circuitry for comparing the voltage across the load to the voltage across the first battery and turning off the series pass transistor when the voltage of the first battery drops below the voltage at the load plus a predetermined offset voltage, which offset voltage is developed by the battery isolator. The battery isolator operates like a diode isolation circuit having a near perfect diode therein.