True® Auxiliary Car Battery Isolator Kit, Heavy-Duty Smart Isolator

(6 customer reviews)


Here is the 12V True® auxiliary car battery isolator kit with a voltage-sensitive relay (VSR), allowing you to mount a auxiliary (or a third!) battery to your car, truck, camper, RV, motorcycle, watercraft, or anything you like.

  • Original heavy-duty battery isolator by True®
  • & guaranteed no volt drop
  • Compact, durable and smarter
  • Free Shipping or visit return and terms policies
SKU: DBK12LARGEHD Category: Tag:


True® Car Battery Isolator Kit composition

  • 1 (SBI) 12V 140A True® Smart Battery Isolator
  • #6 high flex red cable, 20 ft. long, with tinned copper cable lugs.
  • #6 high flex black cable, 3 ft. long, with tinned copper cable lugs.
  • 2 positive battery terminal ends are made of brass alloy.
  • 1 negative battery terminal end with brass alloy
  • 3 loose crimp-on tinned copper cable lugs.
  • 2 segments of adhesive lined shrink tube.
  • 5 zip ties
  • 1 installation manual
  • A 12v battery isolator wiring diagram for car

Product Specifications

  • This heavy-duty auxiliary car battery installation kit is perfect for cars audio system and other general automotive applications.
  • 140 Amps VSR
  • Priority charging for the starting battery
  • Alternator outputs up to 150 amps
  • The True® 12v car auxiliary battery kit employs an entirely automatic battery management system.
  • The 12-volt car battery isolator switch has a quick and easy DIY installation with a wiring diagram.
  • A waterproof car battery isolator switch
  • Shockproof casing, and heat resistant wires with a maximum range of up to 130 degrees for the secure and reliable operation of the accessory battery system.

Delivery: USPS first class or priority mail


The True® 12v second battery kit for car audio uses the most simplistic and modern technology to keep all of your batteries charged, utilizing the engine’s electrical system and isolating the starting battery. Hence, you never get yourself trapped in a deserted area without charge.

The True® dual battery install kit employs the same voltage-sensitive relay that we put in our boat and camper to keep the secondary batteries charged while isolating the starter battery system to keep it charged. The beautiful thing about this is that you don’t have to rewire any alternator wires since they switch charging without you having to do anything!

The auxiliary car battery isolator kit offers the secure charging and isolation of starting and auxiliary batteries across all kinds of cars, RVs, four-wheel drives, campers, trucks, trailers, and even solar purposes. The starting and auxiliary batteries are split when you start the car, allowing you to charge only the starting battery. The voltage-sensitive relay activates when the charge voltage hits 13.3 volts, permitting both batteries to be charged. The light in the upper LH corner is activated to highlight this.

When the engine is turned off, and the battery voltage falls below 12.8 volts, the VSR disengages, isolating the starting and auxiliary batteries. At this moment, the True® 12v auxiliary car battery installation kit will turn the indicator light off and will continue to power any accessories without depleting the starting battery.

The voltage-sensitive relay (VSR) also includes dual sensing tech that monitors the charge of both batteries. As a result, if either battery receives a charge, for example, if a battery charger is attached to the secondary battery, the VSR will activate and charge both batteries. True® technology is renowned for its 12v car audio battery isolator with voltage-sensitive relay (VSR).

The True® car battery installation kits are simple to install and includes the manual and all necessary components. Plus, there’s no need to damage any factory wiring, which could invalidate the manufacturer’s warranty.



(These videos are not endorsed or represented as an “Official Installation video” by True Amalgamated and True Amalgamated accepts no responsibility for its content. It is produced by the end-user as stated. Follow entirely at your own risk.)

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Additional information



6 reviews for True® Auxiliary Car Battery Isolator Kit, Heavy-Duty Smart Isolator

  1. Ray R. Kawal

    To separate an auxiliary battery in my Chevy vehicle, I needed a high-quality relay. Despite being 30 years old, my OEM relay failed. The auxiliary battery is one of two batteries that my pickup camper uses; the second battery is located within the camper.

    I experimented with three different isolation relays, and I thought well of two of them. The Stinger SGP32 was fined because of its lowest coil current, but after doing more research, I discovered this automatic battery isolator relay, which utilizes voltage rather than just an ignition circuit to operate in a clever way. Along with other Smart Battery Isolator, that also looked promising, I ordered one of them. They were nearly identical in design when I got them from Amazon and DFNA, and when I bench tested them, they both performed flawlessly. However, having a water-resistant isolator and LED indicator is an advantage, so I stay with the True brand. 

    Reviewed in the United States on September 4, 2019

  2. reviewforyou

    For it being 2 simple voltage sensitive relays it is a little pricey at $75 bucks. But it works as advertised and does keep the batteries properly charged.

    The only issue I see is that till all batteries in the system drop to about 12.7 volts it does keep them connected. I have mine on a diesel pick-up. I will have to place a heavy diode in the wire somewhere or a switch of some type in the winter due to the truck really needing the minimum of 13.3 volts the start batteries have without this slight issue. They are 14.77 volts at rest, and 13.3 in my use, is like a 12 volt battery being at 11.5vdc.


  3. Jeric Sydney

    This gadget is fantastic and has already saved my life on several occasions! This keeps my primary battery’ isolated from the rest of my car’s electrical system. So even if those items (could) kill the secondary battery, I can still start my car and the isolator will charge the secondary battery. Thanks for saving my budget when I forgot to turn off the inverter at night!

  4. TheThomas

    Between the instructions and the info printed on the motherboard, it was easy to install and feel confident that I know what’s happening

  5. Justin Quiring

    This battery isolator is easy to install

  6. Jesse Steiner

    I’ve been running this battery isolator in my truck for about 4 years now to keep my starting battery separate from my auxilliary battery in my overlanding truck. Performance-wise, I’ve never had any complaints. It works as advertised, and the drop across it when the batteries are in parallel is small.

    However, I went to do some work under the hood recently, and noticed that the plastic housing had become very deformed in the 4 years since I last took a close look at it. It’s all droopy and no longer anything near square. It was mounted under the hood, but not particularly close to the exhaust. It shouldn’t have gotten any hotter than any component under there. To the manufacturer’s credit, it’s still working like a champ. I’m not going to remove it from the system, as it’s still going strong. But I would recommend not mounting in a place that’s likely to see high heat.

    I wouldn’t hesitate to buy another, provided I wasn’t mounting it under the hood of a car.

    Verified Purchase

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