The M-750 Series 36V 310A Dual-Battery Selector & Master Disconnect Switch is ideal for boats, emergency vehicles, buses, heavy trucks, and RVs that use one battery for starting the engine and another battery to power auxiliary loads. This automotive and marine battery selector switch (M-750) has single-pole, triple-throw (SP3T) circuitry, which gives you four options: batteries OFF, battery 1 ON, battery 2 ON, or both batteries ON simultaneously. The battery cutoff position ensures reliable battery disconnection to protect against electrical fire, tampering or theft, and battery drain, while the selector switch positions allow for maximum starting power and backup starting power during emergencies.