1. Battery Chargers
  2. Redarc
  3. Battery Isolators
  4. Vehicle Battery to Auxiliary Battery
  5. DC to DC
  6. 12V
Redarc Smart Start Battery Isolator with Wiring Kit - 12 Volt - 100 Amp

Redarc Smart Start Battery Isolator with Wiring Kit - 12 Volt - 100 Amp

Item # 331-SBI12KIT
lowest price pledge
Our Price: $221.97
You Save: $61.21
Battery Chargers
This item qualifies for Free Shipping
Shipping Weight: 3 lbs
In Stock, Ships Today
Redarc DC to DC Battery Chargers - 331-SBI12KIT
zoom in icon
zoom out icon
Comment field cannot be left empty.
Name field cannot be left empty.

Thank you! Your comment has been submitted successfully. You should be able to view your question/comment here within a few days.

Error submitting comment. Please try again momentarily.

Product Images

This 100-amp dual-battery isolator pulls power from your start battery to charge your auxiliary battery. Isolator switches off to prevent dead battery if start battery voltage drops too low. Compact design for versatile mounting. Wiring included. Call 800-298-8924 to order Redarc battery chargers part number 331-SBI12KIT or order online at etrailer.com. Free expert support on all Redarc products. Guaranteed Lowest Price and Fastest Shipping for Redarc Smart Start Battery Isolator with Wiring Kit - 12 Volt - 100 Amp. Battery Chargers reviews from real customers.
  • All Info
  • Q & A (4)
  • Videos (2)
  • Photos
  • Why etrailer?

Redarc Battery Chargers - 331-SBI12KIT

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

This 100-amp dual-battery isolator pulls power from your start battery to charge your auxiliary battery. Isolator switches off to prevent dead battery if start battery voltage drops too low. Compact design for versatile mounting. Wiring included.


  • Battery isolator protects start battery from auxiliary drain in multiple battery setups
    • Transfers charge from start battery to auxiliary battery once start battery gains charge from alternator
    • Stops charge transfer if start battery voltage drops too low, preventing excessive discharge
  • 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
  • Compact design allows for versatile installation
    • Mount the isolator in a convenient location near the start battery
  • Plug-and-play wiring kit includes:
    • (2) 7-3/4" Long and (2) 70" long positive battery cables
    • 29-1/2" Long ground wire
    • (2) 60-Amp fuses
    • (2) Fuse holders with mounting nuts
    • (2) Battery terminals with protectors
  • Made in Australia


  • Application: vehicles with standard or temperature-compensating alternators
  • Maximum continuous current: 100 amps
    • Standby current: less than 5 mA
  • Output connection: 12V DC
  • Overall dimensions: 3-1/8" long x 2-15/16" wide x 2-1/2" tall
  • Wire gauge: 6
  • 2-Year warranty

With this dual-battery isolator, you can transfer power from your start battery to an auxiliary battery without draining your start battery. As long as your vehicle is on and the alternator is supplying power to the start battery, the Smart Start will transfer some of that power to your auxiliary battery. When your vehicle is shut off, the isolator will separate its connection and stop pulling power. This ensures that your start battery is protected so that no matter how weak your auxiliary battery becomes, your start battery won't be left flat. As a result, 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.

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.

Place the included fuses into the fuse holders and secure one end of each positive (red) cable to the studs on the holders. Then connect the cables to the positive terminals on the start and auxiliary batteries. Securely mount the Smart Start unit and use the free ends on the positive cables to attach each battery to one of the terminals on the Smart Start. Properly connect the ground wire, and ensure that all connections are tight.

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

Redarc Smart Start Battery Isolator Wiring Diagram

SBI12KIT REDARC Smart Start Battery Isolator w/ Wiring Kit - 12 Volt - 100 Amp

Installation Details 331-SBI12KIT Installation instructions

California residents: click here

Video of Redarc Smart Start Battery Isolator with Wiring Kit - 12 Volt - 100 Amp

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Redarc Smart Start Battery Isolator Manufacturer Demo

The Smart Battery Isolator, or SBI, allows your auxiliary battery to charge from the alternator while the vehicle is running, and protect the start battery from discharging when the engine is off. It can also be used in conjunction with an in-vehicle battery charger, or BCDC, to allow the start battery to be jump-started from the auxiliary battery in the event that the start battery is discharged or fails.This product works best with standard alternators, not with smart or variable alternatives. In a dual battery set up where one battery is used as a starter battery to operate the vehicle and one as a secondary to run electrical devices, the SBI ensures your start battery doesn't run flat when you use your secondary battery, while the engine is turned off.When the engine is turned off, and therefore the alternator is no longer running, the start battery will drop below 12.7 volts and the SBI will disengage the secondary battery. This will stop any loads connected to the auxiliary battery from draining the start battery.The Smart Battery Isolator comes in 12 and 24 volt, both 100 and 200 amp models, and a dual sensing range is also available. You can pair the Smart Battery Isolator with in-vehicle battery chargers, which will allow the start battery to be jump-started from the auxiliary battery in the event that the start battery is discharged or fails.When programmed as a low disconnect isolator, it can also be paired with battery management systems to protect the auxiliary battery from excessive discharge. The Smart Battery Isolator is ideal for four-by-fours, motor homes, marine craft, and heavy industrial vehicles.(silence).


Ask the Experts about this Redarc Battery Chargers

  • Does The Manager30 Replace Solar Panel Controller
    Yes, the The Manager30 Battery Management System with Lithium Profile # 331-BMS1230S2-NA takes place of the solar controller for your current solar panel system. Solar panel controllers are used to help manage the power coming in from the panels and since The Manager30 does the same thing it actually can't be installed with a solar panel controller. The Manager30 is definitely an upgrade though as it pulls power from the solar panels and your vehicle start batter (via the alternator). It...
    view full answer...
  • Battery Charger Recommendation to Charge Trailer Battery from Alternator and Solar Panel
    The Redarc In-Vehicle BCDC Battery Charger # 331-SBI12KIT that you referenced can manage input current from a solar panel and an alternator as well as 12 volts to 24 volts so you'd be totally fine to use this. You would not be able to reverse the flow of the charge though and go from the battery bank you are charging back to the vehicle. It only allows charging in one direction. I attached a chart that shows how this wires up as well.
    view full answer...
  • How to Wire Two 6 Volt Batteries to a 12 Volt Battery
    I attached a picture that shows how to run batteries in both series and parallel. You will need to wire up the two 6 volt batteries like the picture on the left so that they would be in series and at 12 volts. To connect a 12 volt battery to that circuit you would need to run the positive post of the 12 volt battery to the positive side of the battery run on the in series batteries. Not the one that is connecting the two batteries, the one that would be the output of the two in-series...
    view full answer...
  • How to Determine if 2016 Jeep Cherokee Has Smart Alternator
    From what I could find it doesn't look like a 2016 Jeep Cherokee has a smart alternator, but you can (and should) still do a little test on your own to determine if the Redarc Smart Start Battery Isolator with Wiring Kit # 331-SBI12KIT is necessary for the installation of the Redarc In-Vehicle BCDC Battery Charger # 331-BCDC1225D. To determine if your Cherokee has a smart alternator you just need to measure the amount of volts it has, using a multimeter # BTMT15, after leaving the engine...
    view full answer...

Do you have a question about this Battery Charger?

  • Why etrailer.com?

    At etrailer.com we guarantee:
  • Highest quality battery chargers for the best price.

    Our Lowest Price Pledge ensures you will never overpay for the parts you need.
  • Real product know-how.

    We make sure that the products we sell are what we say they are, and that they work the way they are supposed to work. Get real advice from a real person who has the knowledge and expertise needed to solve your problem.
  • Most detailed, accurate battery charger information available.

    Because we take providing accurate product information seriously, we take our own detailed product photos, demo videos and installation videos, as well as verify measurements, instructions, and vehicle fit information.
  • Installations, made easy.

    We love helping people and have the most highly-trained customer service, hands-on experience, step by step videos and installation instructions.
  • Fast shipping.

    Your order is automatically routed to get out of our warehouse and to your door as quickly as possible. Receive free shipping on orders over $99.
  • Personalized service for life.

    We provide one-on-one, personalized service from the ordering process through the life of your product.
  • Trusted since 1946.

    We've been serving customers since our parts store first opened in 1946 and continue to be recognized by our customers, our vendors and third parties for exceptional service.
  • Returns Policy

    Need to return an item? No problem. Please read our Returns Policy for more information.

Info for this part was:

Edited by:
Lindsey S
Installed by:
Jeff D
Expert Research:
Jameson C
Video Edited:
Chris R
Written by:
Brian T
Updated by:
Kristina F

At etrailer.com we provide the best information available about the products we sell. We take the quality of our information seriously so that you can get the right part the first time. Let us know if anything is missing or if you have any questions.

Product Experts Available Now!

Call 800-298-8924