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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
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Redarc 12V Battery Charger - 331-SBI12KIT
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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 charger 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 Charger reviews from real customers.
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  • Reviews (3)
  • Q & A (6)
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  • Why etrailer?

Redarc Battery Charger - 331-SBI12KIT

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

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

Customer Reviews

Redarc Smart Start Battery Isolator with Wiring Kit - 12 Volt - 100 Amp - 331-SBI12KIT

Average Customer Rating:  5.0 out of 5 stars   (3 Customer Reviews)

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.

- 331-SBI12KIT

It's for my 04 Jeep Wrangler TJ. 870505

- 331-SBI12KIT

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. 819673

- 331-SBI12KIT

Awesome product, easy to install and come with all parts needed to install second battery!!! 791000


Ask the Experts about this Redarc Battery Charger

  • 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...
  • 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...
  • Recommended Battery Isolator for In-Bed Camper on 2006 Dodge Ram Pickup
    Thank you so much for all of the info! The Tow Ready Battery Isolation Solenoid # TR118665 does serve it's purpose but I do understand the need for something that is able to do a bit more. The best solution that we have to offer is the Redarc Smart Start Battery Isolator with Wiring Kit # 331-SBI12KIT because it allows you to install the isolator in-between the start and auxiliary batteries instead of having to install it between the alternator and batteries (it is recommended to...
    view full answer...
  • Can Redarc In-Vehicle BCDC Battery Charger be Used to Jump Start Battery
    In addition to the Redarc In-Vehicle BCDC Battery Charger # 331-BCDC1225D you need to use a Redarc Smart Start Battery Isolator. I recommend using the Battery Isolator with Wiring Kit # 331-SBI12KIT if you don't already have the fuse kit, or part # 331-SBI12D if you do already have the fuse kit. With the isolator installed you can then connect a push-button into your system to help jump your start battery.
    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...

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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

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