An automotive electrical system produces enough electrical power for an automobile to run the ignition system, charge the battery again and supply power for electronic devices inside the vehicle.

Some vehicles take advantage of this extra electrical capacity to sustain a 2nd on-board battery. Typically a vehicle with more than one battery will include a battery isolator in the set up.

A battery isolator separates the batteries from one another in a way that allows the charging source to charge them in a designated order.  This isolator will not only manage the charging sequence order but also separates (isolates) the batteries from discharging each other if and when the charging source is not producing adequate power. In addition, a battery isolator kit assures that the vehicles electrical system is protected from surges during start-up or at other times when a large spike or variance in voltage/amperage may occur which could lead to a risk of electrical system failure. A trouble-free setup is one in which the vehicle contains 2 batteries connected in parallel through the isolator. 

The TRUE dual battery isolator system is not linked to the vehicle's alternator or its ignition but instead relies on "smart circuitry" which senses the voltage available to determine when to connect or isolate the batteries.  This avoids having to rewire the alternator or connect to the ignition. By using smart technology the dual battery isolator kit keeps things simple and more efficient.

How battery isolator works diagram   

How Battery Isolator Works in Your Vehicles


To determine if an isolator is functioning properly you will want to use a volt meter to check the voltage on both sides of the isolator while the engine is both running and not running.. The following common how to check a battery isolator steps are provided by the experts at

  1. Set your volt meter to DC voltage
  2. Touch the meters black probe to negative terminal of the battery or other common ground.
  3. Touch the meter's red probe to the battery's positive terminal.
  4. With the engine NOT running the reading should be somewhere in the 12.7 volt range. 
  5. Now start your engine.  Immediately apply the meter to the (primary) starting battery.  You should see the voltage rising from 12.3 or so upward.  When the voltage meter reaches 13.2 volts the isolator will activate (indicator light illuminates)
  6. Once the indicator light is illuminated you should have the same voltage reading (13.2 or greater) on both batteries verifying that the battery isolator has closed.
  7. Now turn the engine off.  Apply the voltmeter to the primary battery.  The voltage will slowly drop to a level or resting voltage of around 12.7.  When the voltage drops to 12.8 or lower the isolator will disconnect and the indicator light will go off.
  8. Repeat the process but immediately when the vehicle is started apply the meter to the secondary battery.  Before the isolator's indicator light illuminates the voltage will read 12.7 or so.  When the isolator illuminates the voltage will raise to above 13.2 thus verifying that the system is fully functional.

    (Call us now if you are still confused on how to check your dual battery isolator?)

How to wire the Dual Battery Isolator

The isolator from is the simplest of all isolators to install.  The “dual sensing” feature of this battery isolator makes it impossible to install backwards.  Wiring is accomplished by:

  1. Connect a cable from the positive terminal of the primary battery by removing one of the nuts of the threaded studs on the back of the isolator.  Apply cable, replace nut and tighten securely.
  2. Then connect a second cable from the isolator's remaining threaded stud to the positive terminal of the second battery. 
  3. The isolator's black ground lead must then be connected to a common ground shared by all batteries.  This can be a frame ground or can be connected directly to the batteries.  NOTE:  All batteries and the isolator must share a common ground or nothing will function.  Wiring dual battery isolator is provided by

The isolators provided on are voltage sensitive relays with smart technology that makes them simple in application but provide more efficient operation through elimination of the large diodes in other isolators.  These diodes rob large amounts of important charging voltage, produce a large amount of heat and eventually burn out because of it.  If you need information on application of other types of isolators you can find it by searching online for multi battery isolator wiring diagram.

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