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The advantages of using a high current VSR are that it will cover your dual battery charging requirements and emergency parallel operation in one unit. Remote emergency parallel function: The 701-MDVS and 720-MDVS can be operated through a momentary button on the dash which will parallel the batteries for a preset time of 10 minutes. Once this 10 minutes has passed, if the voltage is up high enough for the voltage sensitive switch to operate, it will stay engaged. If not, it will disengage. Engine run sensing: VSR will engage when the voltage on either start or house battery reaches 13.7 volts. If the combined battery voltage drops below 13.0 volts and the engine is not running, after 5 seconds the contacts will open and stay open until the start or house battery voltage exceeds 13.7 volts. If the combined battery voltage drops below 12.2 volts and the engine is running, after 5 minutes the contacts will open and stay open until the start or house battery voltage exceeds 13.7 volts. If voltage drops below 13 volts and stays above 12.2 volts on either start or house battery while engine is running, the VSR will stay engaged.