Cole Hersee battery isolators are important safeguards for multiple circuit battery electrical systems.

Many DC electrical systems have more than one battery connected to one or two alternators. The most common system consists of two batteries and one alternator. This type of system can be found in

Ambulances Fire Trucks Police and Emergency Vehicles Buses Motor homes and Trailers

Boats Tow Trucks Vans & Service Vehicles Snow Plows Salt & Sand Spreaders

How a typical system operates
When two batteries supplying separate circuits are connected to a single alternator, the primary battery is usually connected to the engine starting system with the auxiliary battery connected to other electrically powered equipment.

The auxiliary equipment could be emergency lights, refrigeration, a motor home or trailer electrical system, pumps, lifts, or life support equipment in ambulances.

When the engine and alternator are operating, there is enough power to supply the electrical equipment and keep both batteries charged. When the engine and alternator are not operating, the auxiliary battery is supplying the power to operate the equipment. But, since the batteries are connected, the primary battery is being drained as the auxiliary battery uses its charge. The batteries tend to act like fluid reservoirs, keeping an equal charge level. As a result, the primary battery could drain to the point where it would not start the engine when required.

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