Boaters have always had a need for extra appliances and equipment...

Once you've got a second battery, Cole Hersee has the way to make the batteries work together...

Battery Isolators

Wiring information: IF-128

Background info on two-battery systems

Applications: vehicles that use Battery Isolators

What kinds of Battery Isolator does Cole Hersee make?

How do Battery Isolators work?

Why the increasing interest in two-battery systems?

Why use a Battery Isolator?

Background info:
Two major kinds of battery:
Starting battery and Deep-cycle battery

We're all familiar with the starting battery (the same type that we have in our cars)… and its limitations! Drawing down this type of battery to a low charge results in a significantly lowered battery life. It is designed to give a strong burst of energy at infrequent intervals (when you start the vehicle). It's not the best way to power other equipment that has a significant draw.

The deep-cycle battery is designed to have opposite characteristics: it can support a heavy drawdown, and can be repeatedly recharged. It is not suitable for providing the sudden heavy surge of power required for ignition.

See a useful article on deep-cycle batteries from Heavy Duty Trucking.

Why the surge of interest in two-battery systems?
With federal changes in wheelbase regulations, truck tractors no longer need to be as short as they were previously. If you've visited a truck show recently, you'll see how big the cabs have become. With the 'cab-condos' there's been a demand for extra domestic appliances. If you don't idle the engine, there's a growing need for extra power for all those refrigerators, TVs, VCRs, microwaves and computers.

See a useful article on deep-cycle batteries from Heavy Duty Trucking.


Why use a Battery Isolator?
So now you've got two batteries and one means of charging the batteries. If you connect them all together the batteries drain from the one with the higher charge into the one with the lower charge until they're equal. That's not too bad for a deep-cycle battery, but it's disaster for a starting battery, because you might have insufficient power to start the engine. You might also be drawing down too deeply on your starting battery, which will lead to premature failure.

The option is to create two independent circuits, each controlled by an On-Off switch (we've got lots of these at Cole Hersee!) or a battery selector switch. If you're a methodical person, this could be OK for you. You have to remember to charge up both batteries in due course. With a Battery Isolator, you can forget this problem.

What kinds of Battery Isolator does Cole Hersee offer?
Check them out. Cole Hersee has a good selection of Isolators.

Master Catalog page 140
Marine Catalog page 11
Online catalog

48080 42A
48070 70A
48090 90A
48120 140A
48160 200A
48161 250A, using Schottky diodes to comply with federal KKK-A-1822b for ambulances.
48092 90A for use with Delcotron alternators
48122 140A for use with Delcotron alternators
48162 200A for use with Delcotron alternators


Two battery systems are common
in these applications:

Boating
More boats are adding sophisticated electronic equipment, as well as refrigerators (and other heavy power demand appliances)

Emergency vehicles
Extra lights, sirens, medical equipment

Special purpose vehicles
with ancillary power equipment
The EZ-GO "Refresher"

How does a Battery Isolator work?
Simple. It's an electronic sealed unit that contains two diodes.

Diodes, if you remember, permit current to flow in one direction only. Power supplied to the middle stud of the Battery Isolator flows to each of the other studs. Current cannot flow back from one of the batteries to the other battery. Charging current flows preferentially into the battery with the lowest charge (because of the higher potential difference).

Because they're solid state, isolators have a long life. They're not susceptible to contaminants, vibration, or extremes in temperature

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