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Redarc Smart Start Battery Isolator - Dual Sensing - 12 Volt - 200 Amp

Redarc Smart Start Battery Isolator - Dual Sensing - 12 Volt - 200 Amp

Item # 331-SBI212D
Our Price: $325.00
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Connect this isolator in-line with 2 batteries - 1 that is charged by your alternator and another that connects to an outside source - and it will transfer power in either direction to keep both batteries charged. Shuts off if battery drops to 12.7V. 1-800-940-8924 to order Redarc battery charger part number 331-SBI212D or order online at Free expert support on all Redarc products. Great prices and Fastest Shipping for Redarc Smart Start Battery Isolator - Dual Sensing - 12 Volt - 200 Amp. Battery Charger reviews from real customers.
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Redarc Battery Charger - 331-SBI212D

  • Battery Isolators
  • 12V
  • Vehicle Battery to Auxiliary Battery
  • Redarc

Connect this isolator in-line with 2 batteries - 1 that is charged by your alternator and another that connects to an outside source - and it will transfer power in either direction to keep both batteries charged. Shuts off if battery drops to 12.7V.


  • Dual-sensing battery isolator connects in-line with 2 batteries and transfers power in either direction
    • Transfers charge from start battery to auxiliary battery once start battery gains charge from alternator
    • Pulls power from auxiliary battery that is connected to outside power source to charge start battery
  • Isolator function stops power transfer from the charging battery if its voltage drops too low
    • Prevents excessive discharge and dead battery
  • Override wire allows for emergency starts and simple fault detection
    • Attach to a switch (sold separately) to manually reverse charge and jump-start a dead start battery
    • Connect to an LED (not included) that can be mounted in your cab for easy viewing of diagnostics
  • Silver contact points ensure long life and corrosion resistance
  • Durable housing protects sensitive electronics
  • Compact design allows for versatile installation
    • Mount the isolator in a convenient location near the start battery
    • 4-Gauge cables, fuses, and connectors sold separately
  • Made in Australia


  • Application: vehicles with standard or temperature-compensating alternators
  • Maximum continuous current: 200 amps
    • Standby current: less than 5 mA
  • Output connection: 12V DC
  • Overall dimensions: 3-15/16" long x 3-3/4" wide x 3-1/2" tall
  • 2-Year warranty

This dual-sensing battery isolator can transfer charge from either your start battery or your auxiliary battery to keep both batteries in your setup charged. Turn on your vehicle, and once the alternator begins to supply power to the start battery, the Smart Start will transfer some of that power to your auxiliary battery. If your start battery is low, make sure that your auxiliary battery is connected to an outside power source, like a solar panel, and it can transfer some of its charge to the start battery. The isolator function of this system will stop the charge transfer to and from either battery if the charging battery's voltage drops too low. This ensures that both batteries are protected so that you can venture out without the fear of running into a dead battery.

Parallel Charging for Optimal Functioning

REDARC Smart Start Dual Sensing Battery Isolator Parallel Charging Setup Diagram

The Smart Start connects in-line between your start battery and the auxiliary battery. This way it can pull the charge directly from the battery instead of pulling from an outside source, like your vehicle's alternator. This method of charging is called parallel charging.

REDARC Smart Start Dual Sensing Battery Isolator Priority Charging Setup Diagram

Most other battery isolators on the market use priority charging. In a typical priority charging setup, the alternator provides charge to either the start battery or the auxiliary battery, but not to both simultaneously. This can leave both batteries underpowered. With parallel charging, the power is drawn directly from the start battery, which removes stress on the alternator because it doesn't have to manage both batteries separately. This streamline connection of the Smart Start to the start battery also prevents potentially damaging voltage surges that can occur when a priority charger switches over between batteries.

2-Way Charging

Dual-sensing technology allows this Smart Start isolator to monitor the voltage of both the start battery and the auxiliary battery. If the auxiliary battery is connected to an external power source, then the Smart Start will recognize when the auxiliary battery reaches a full charge (13.2V) and it will redirect the current to provide a charge to the start battery. This allows you to use a solar panel (sold separately) or an additional battery charger (sold separately) to charge not only the auxiliary battery, but also the start battery.

Additional Features

The blue override wire attached to the Smart Start allows for additional features, like the Start Assist function. This function allows you to jump-start a dead start battery using the auxiliary battery. Just connect the blue wire to a push-button switch (sold separately) to create a bridge of power from the auxiliary battery to your dead battery. Great for those mornings when you leave the radio on too long or forget to close the vehicle door.

You can also connect the blue wire to an LED (not included) to create an in-cab fault indicator. There is an internal LED on the unit itself that provides fault detection. This system communicates by causing the LED to flash a certain number of times to indicate errors. For example, 2 flashes signals over-voltage, and 3 flashes signals a voltage drop or excessive current draw fault. By connecting an additional LED to the blue wire, and running that up to your cab, you can more quickly assess these faults than if you had to peer into your engine compartment to see the light on the unit itself.

For assistance in wiring the Smart Start to include these optional features, please refer to the diagrams below:

Redarc Smart Start Battery Isolator Optional Wiring

Compact Design for Versatile Mounting

Mount the battery isolator in a location near your vehicle's start battery. The compact design of the unit allows you to have a good deal of flexibility when selecting a mounting location. A couple of places to consider would be in front of the radiator or behind the headlight assembly. You will need to make sure that the location you choose is not exposed directly to engine heat.

Once the unit is securely mounted, attach each battery to one of the terminals on the Smart Start. It is important to use the proper gauge wire for your particular application. If the cable length that you need is under 10', make sure that the wire gauge is 4 AWG. If you will be using between 10' and 20' of cable, you will want to select a thicker 3-gauge wire. To prevent damage from overload and short circuits, you will want to use properly rated fuses or circuit breakers (sold separately) to ensure that current is efficiently transferred.

For assistance in properly wiring the Smart Start, please refer to the diagram below:

REDARC Smart Start Dual Sensing Battery Isolator Wirisng Diagram

SBI212D REDARC Smart Start Battery Isolator - Dual Sensing - 12 Volt - 200 Amp

Installation Details 331-SBI212D Installation instructions

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Customer Satisfaction Score:

Customer Reviews

Redarc Smart Start Battery Isolator - Dual Sensing - 12 Volt - 200 Amp - 331-SBI212D

Average Customer Rating:  5.0 out of 5 stars   (22 Customer Reviews)

Connect this isolator in-line with 2 batteries - 1 that is charged by your alternator and another that connects to an outside source - and it will transfer power in either direction to keep both batteries charged. Shuts off if battery drops to 12.7V.


I didn’t know this product existed. I don’t know why RV manufactures don’t install these when they build the motor homes. Always a pleasure doing business with e-trailer.


I purchased the Redarc 331-SB1212D battery charger during the 2018 Christmas holiday season, it shipped with good efforts from etrailer. It is installed on a 2009 Chevy 5500 diesel powered cab and chassis truck , 2 on-board factory batteries in combination with add on 2 battery auxiliary bank, chassis mounted. I have extra heavy auxiliary power leads wire loom insulated routed with 350 amp Anderson connectors located at the ends , 1 lead to the front bumper , 2 leads to the rear bumper and a small 2/0 lead routed to the cab with 175amp Anderson connector for a 650 watt inverter. This application provides jumpstart service and remote power for dump trailer and 3000watt inverter power . This system has an additional provision to combine all batteries for heavy winching or sub zeros self jumpstart . My installer provided the additional switching to Redarc design specification.


With a flip of a switch from the drivers set, I'm able to re-charge the coach batteries from the vehicle battery via this Redarc Battery Charger while driving to the next camping adventure.


This bad boy had me at dual sensing, and 200 amps is exactly what I need for my beefy house battery bank. One knock might be a short ground wire, but otherwise great product.


I have used these redarcs a couple of times with great success but having this shipped in a very timely fashion from etrailer is fantastic!


Product works as expected and I would recommend it to anybody needing a product like this.


Great product, great service.



Really like this isolator. Replaced two Cole-Hersey Isolators that failed prematurely in a Class C RV after only 11 and 3 months. Second photo shows Cole-Hersey replaced by Redarc shown in last picture


I put this on a 2013 chevy HD 4 wheel drive and it works very well.
I have my main battery went bad and I open the hood and flip the switch and the
accessory battery started my truck. thank you for having good products for us to buy
when we need something,


I use this in my Jeep to keep my second battery for accessories charged and ready. After a year of having it installed I couldn’t be happier with the product. I have spoken with the folks out in Australia at Redarc and find them to be very awesome to speak too.


Wonderful instructions, plenty of wire, and a very good product. Will try and update this review in a year! Thanks for putting the pieces together. All solid quality, 60 amp fuses, and neatly trimmed heavy gauged wire.


This is a great product. I use it to run my fridge in my Jeep to keep the second battery charged.


works great would but anain


It's for my 04 Jeep Wrangler TJ.


works prefect


Works great


Awesome product, easy to install and come with all parts needed to install second battery!!!


Got exactly what I needed and very fast.





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