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Top 4 Best 12V DC Dual Battery Isolator In 2023 Review & Buying Guide

Having a dual battery isolator in your 4WD or commercial vehicle can be a lifesaver. Nobody wants to be stuck off-road or on the side of the highway because of a flat battery. Keeping a backup power supply is almost a necessity.

Isolators are very clever these days. In-built sensors draw power from the strongest battery, while the idle battery is charged from the alternator. It also knows to switch power sources if one battery suddenly dies.

So we decided to take a look at four of the very Best 12V DC Dual Battery Isolators currently on the market. So, join us as we go through them and find the perfect 12V DC dual battery isolator for you…

Top 4 Best 12V DC Dual Battery Isolator In 2023 Review & Buying Guide

Top 4 Best 12V DC Dual Battery Isolator In 2023 Review

  1. Blue Sea Add-a-Battery 120A – Best 12V DC Dual-Battery Isolator with Switch
  2. WirthCo Battery Doctor 150A – Most Versatile 12V DC Dual Battery Isolator
  3. KeyLine Chargers 140A – Best Complete 12V DC Dual Battery Isolator Kit
  4. JayCorp True Smart 140A – Best Simple 12V DC Dual Battery Isolator

1 Blue Sea Add-a-Battery 120A – Best 12V DC Dual-Battery Isolator with Switch

The Add-a-Battery can act as both an on/off switch or manage switching and charging of two batteries from a single charge source. This system can be used with both cars and boats for providing that all-important backup.

The package consists of a separate switch and isolator unit. The switch itself is a large rotary dial with clear labeling. Options include OFF with the arrow pointing straight up, ON pointing to the right, and combined pointing down.

Automatic relay circuit…

Thanks to the 12/24V DC 120A charging relay, batteries automatically combine during charging. It will also automatically isolate the batteries during engine cranking and when there is no charging.

Because of this technology, the charge between two batteries can be shared more efficiently than standard isolators. Now your switching can be simplified, your engine isolated, and circuits housed.

Quality components…

Tin-plated copper studs are used to provide maximum conductivity. Additionally, this helps to prevent corrosion. Perfect for use in either a 4WD or boat, as they are often exposed to various elements and environments.

Once the installation is finished, all you need to do is switch your battery to ON when you arrive and OFF when you leave. The build quality and easy to follow instructions included with this device make it a worthy investment.

Blue Sea Add-a-Battery 120A

Our rating:4.8 out of 5 stars (4.8 / 5)


  • Switch included.
  • Automatic charging detection.
  • High build quality.


  • Wiring, fuses, and grounding required.
  • Takes several hours to install.

2 WirthCo Battery Doctor 150A – Most Versatile 12V DC Dual Battery Isolator

For our next product, we have this isolator manufactured by WirthCo called the Battery Doctor. Unlike the Add-a-Battery, this product is a stand-alone isolator and does not include a switch.

This state-of-the-art, fully automatic, dual battery controller is suitable for any vehicle requiring an auxiliary battery. The unit itself is suitably small and lightweight, making it easy to install and mount in a convenient location.


With a single press of the override/reset button, the batteries switch out of master and auxiliary mode. The batteries then engage parallel mode combining their power, perfect for when jump-starting is necessary.

Employing electronic switching control technology allows for the charging of two batteries from a single alternator. The second battery receives a charge from the alternator while the starter battery remains isolated.

Suitable for a range of vehicles…

Being water-resistant means that this isolator is suitable for both marine applications and 4WD off-road vehicles. Offering a resistance rating of IP62 ensures protection from both water and dust.

A mounting bracket is included to assist with installation. There is also built-in over current and surge protection making the isolator suitable for vehicles with sensitive electronic systems. This isolator is suitable for almost any vehicle.

WirthCo Battery Doctor 150A

Our rating:4.5 out of 5 stars (4.5 / 5)


  • IP62 water and dust resistance.
  • Mounting bracket included.
  • Over current and surge protection.


  • Compatibility issues with solar systems.
  • Indicator light takes a long time to switch off.

3 KeyLine Chargers 140A – Best Complete 12V DC Dual Battery Isolator Kit

This isolator from KeyLine called Chargers comes with everything you need for installation. In the package, you receive a relay, a 20 feet (6 meter) red cable, a 20 feet (6 meter) black cable, a pair of positive brass terminals, a negative brass terminal, lugs, and heat shrink.

Because of the cutting edge programming, you will be offered optimum performance with zero sacrifice. The ultra-small design allows this isolator to be mounted almost anywhere, including under the hood of your vehicle.

Can handle almost anything…

The isolator is tightly secured with a four screw mounting system and silicone coated cushion. This provides the ultimate vibration protection. Perfect for use in a 4WD that frequently travel across even the most rugged terrain.

An IP65 water and dust resistant rating allows for travel almost anywhere. Rain, mud, dust, dirt, and even sand is no problem and will not affect performance. No matter where you go, the KeyLine will be performing alongside you.

Easy to install…

Simple as power wire in, power wire out. It can’t get any easier than that. This isolator is suitable for use in a wide range of applications. It can be used for ATVs, boats, RVs, campers, off-road vehicles, and more.

The kit comes with easy to read, foolproof instructions. Anybody with a basic knowledge of wiring can have this installed in roughly 15 minutes, even if you use solar as an additional source of power.

KeyLine Chargers 140A

Our rating:4.6 out of 5 stars (4.6 / 5)


  • Everything you need for full installation.
  • Easy to follow instructions.
  • IP65 rated water and dust resistance.


  • No reset or override switch.

4 JayCorp True Smart 140A – Best Simple 12V DC Dual Battery Isolator

The final model we have for you is the True Smart from JayCorp. It is ultra-simple yet still technologically advanced. VSR (voltage sensitive ready), this isolator is ready for use in any 4WD, boat, RV, or any other area, and an additional battery is required.

In the package, you receive the isolator unit, some mounting hardware, and an instruction booklet. Connections are made at the rear of the device, and it is compact enough to be mounted almost anywhere.

Looks simple, behaves smart…

Although this looks very basic, the isolator will sense both batteries. If either one is receiving a charge, it will allow charging of both. Once no more current is being supplied, it will isolate them.

This isn’t an old-fashioned isolator that uses diodes to reduce the amount of current and requires large heatsinks. Instead, a relay is used that can open and close with no energy loss due to internal resistance.

And that’s not all…

When the engine is running, its charging source raises the voltage of the start battery. The isolator engages and connects the two batteries to charge simultaneously. The built-in LED light will then glow blue.

Once all the voltage drops, the isolator will disengage, and the blue LED will turn off. This indicates that the batteries are separated, therefore preventing the start battery from being drained by the use of power from the second battery.

JayCorp True Smart 140A

Our rating:4.7 out of 5 stars (4.7 / 5)


  • Simple, compact design.
  • Mounting hardware included.
  • Affordable option.


  • Small size prevents larger gauge wires being used.
  • No water or dust resistance.

Best 12V DC Dual Battery Isolator Buying Guide

KeyLine Chargers 12V 140 Amp Dual Battery Isolator Voltage Sensitive Relay (VSR) Pro Dual Battery Kit

We have just reviewed four very different versions of excellent isolators that are currently on the market. Each of these products is capable of regulating and protecting power to a second battery. And all of them can be used in a variety of applications.

But which of these products will suit your needs the best? Next, we will compare the strengths and weaknesses of each of these products to ensure you make the best decision with your purchase.

Which Vehicle?

Most of these products can be installed in almost any boat or vehicle. However, some will suit particular ones better than others. Obviously, if you will be installing into a marine craft, you will want something waterproof.

All except the JayCorp offers water resistance. The KeyLine does offer the highest rated resistance, though with IP65 certification. The Blue Sea also includes a switch to completely cut off power.

Planning Your Installation

The size and shape of the isolator will have a significant impact on where it can be mounted. If you wish to install the isolator under the hood of your vehicle, for example, something more compact will be easier.

One of the most compact isolators is the JayCorp True Smart. It is easy to install; however, it is missing the water and dust resistance rating. With a quick application of silicone, this can easily be rectified, though.

If, by now, you are still having difficulty deciding on which product to choose, stick around. Next, we will reveal what our choice is for the best overall 12V dual battery isolator and why. But before that…

Are You LookingFor More Superb Products To Manage Electrics?

 Blue Sea Systems Add-A-Battery Kit

If so, we recommend looking at our Best Battery Backup Reviews, our Best Wall Mounted Surge Protectors Review, and our Best Electricity Monitor Reviews for the ultimate electrical management for home and business in 2023.

And when it comes to handy adapters, cables, and other items to keep around, you may also want to check out our Best Magnetic USB Charging Cables Review, our Best Wireless HDMI Transmitters Receivers Review, our Best Right Angle HDMI Adapter Reviews, our Best Solar Chargers Review, or our Best USB HDTV Tune Reviews?

Back to the best 12V dual battery isolators…

So, What Is The Best 12V DC Dual Battery Isolator?

In order to decide on which product deserves the title of the best, we have taken the following into consideration. It must perform well, offer useful features, and represent excellent value. The one we feel meets all these requirements to the highest degree is the…

KeyLine Chargers 140A

It performs exactly as it’s supposed to, offers water, dust, and vibration resistance, and comes complete with everything you need.

Happy charging!

About Paul S. Brunet

Known as the "Tech Lover", Paul is an expert of current and trending technology. Here at TinyGrab, he makes "tech" easy to understand for the average person.

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