Pre-wired module combining 113557 Mini Battery Selector Switch and a dual sensing Voltage Sensitive Relay. With the selector switch in position 1, it becomes the sensing battery for the VSR. When the engine is first started the relay is open and remains open until the selected battery reaches a preset 13.4 volt. The relay closes at the rated voltage providing charge to both batteries. When the selected battery voltage drops below 12.8 volt, the DVSR disengages, separating the batteries and ensuring that battery 1 is not discharged by house loads. When the selector switch is in position 2, this becomes the sensing battery and the reciprocal occurs. When the selector switch is in the both position the DVSR is inactive and the charge and load is distributed evenly between the batteries. With this system the loads are run off the same battery as the engine starting battery.