Best Battery Isolator

Last Updated on September 1, 2020

Are you searching for the best battery isolator?

I have used a number of battery isolators in my van and RV and having a high quality model is important. Low end isolators perform poorly and the headaches they caused were not worth the savings. With this in mind I have reviewed the top battery isolators on the market today and after reading this article you will know my recommendations.

Check the quick list below for links to customer reviews and prices for my best battery isolator picks, or read on for the full review:

  1. 12V 140 Amp Dual Battery Smart Isolator by KeyLine
  2. JayCorp Smart Dual Battery 140A Isolator (VSR Voltage Sensitive Relay)
  3. Cole Hersee 48120 Battery Isolator
  4. WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator
  5. True UTV-SBI-CM UTV Dual Battery Isolator Connect & Monitor Kit

Battery isolators split direct current and prevents current from flowing in more than one direction. This means that you can take energy from a number of batteries without worrying about the flow of electricity. They are common in RVs and allow users to have one battery for running appliances and another for starting the motor. Battery isolators also keep your batteries from draining each other when they are all charged from a single alternator.

How to Choose the Best Battery Isolator

One thing that you must consider when shopping for a battery isolator is whether you want a diode-based or relay-based isolator. Diode-based isolators contain older technology than relay-based isolators.

Relay-based isolators generally don’t have any voltage drop when they are used but diode-based isolators will. The amount of the drop depends on how much current is passing through the isolator. When you run more current through the isolator, the you are going to experience a larger drop, making it much less efficient to charge your battery.

The Benefits of a Battery Isolator

A great battery isolator will ensure that you can hook up two, or more, batteries to your alternator. You will be able to isolate your starting battery and keep the current separate from your second battery.

Additionally, when you use your battery isolator, you can easily adjust the batteries to be in parallel mode. This makes it possible to jump start your vehicle. I find this is very important when you are in an emergency situation and your RV or car won’t start as you can handle jump starting the battery on your own without having to rely on another person for help.

When you have a great battery isolator you are investing in battery insurance for your primary battery. When you use other appliances that drain your battery, your alternator may simply not be able to keep up with the demand. However, a quality battery isolator can connect two batteries to your alternator, which lets you run one battery to start and power your vehicle while using the other to power your other electronic items.

What to Look

It’s important that you take time to choose the best dual battery isolator for your needs. I know that it can be overwhelming when you’re shopping, especially if you aren’t sure what kind of isolator will work best in your vehicle, specifically in an RV. However, there are a few things that you should consider to help you make the best decision for your set up.

First, you need to make sure that you consider the size of the isolator. You have to ensure that it has an amp rating that is at least as high or higher than your peak output. This is the only way to be sure that it will work correctly with your alternator.

I also recommend that you make sure to consider the components shipped with your isolator. It can be tempting to use your own wiring but it’s smart to use ones that are the right size for your connection distances. This ensures not only that your isolator works correctly but also that it is safe to use without overheating.

Some auxiliary battery isolators offer surge protection, which is something that everyone needs. This ensures that your electronics won’t be damaged by a battery surge when you’re on the road.

How to Use Your Battery Isolator

Once your battery isolator is installed correctly, then you really don’t need to do anything to it to keep it working the way that it should. I do recommend that you take time to test it periodically to ensure that it works correctly, especially if you use your RV without electrical hookups when camping.

Testing your isolator is easy when you use a multimeter. Simply start your engine and then use the multimeter to check your voltage coming from the alternator as well as going to the battery. Doing this on a regular basis will give you peace of mind when you’re on the road.

If there is a problem where your battery isn’t charging the way that it is supposed to, then you need to check not only the ground connection but also the battery connection. There are some vehicles that tend to have a lot of corrosion in battery connections, which can cause the isolator to not work nearly as well as it should.

If you find corrosion clean it with a wire brush, then you will want to test your isolator again to ensure that this has taken care of the problem.

Precautions When Using Your Isolator

Any time that you are going to be completing electrical work on your own, you may be putting yourself in danger and need to take some precautions. Installing a battery isolator is the most dangerous time that you are going to be using it but once it is installed correctly, you never need to worry about its safety.

You need to make sure to follow the included manufacturer instructions with your new battery isolator so that you can be sure that you are safe.

Best Battery Isolators

12V 140 Amp Dual Battery Smart Isolator by KeyLine

This isolator is IP65 Certified, which means that it can safely be used in wet, dusty, and extreme weather environments without any problems. Additionally, it comes with mounting hardware and a mounting plate so that it can easily be installed without relying on professional help. It has a voltage-sensitive relay that means that it will cut out at 12.8 V and in at 13.3 V, ensuring that your vehicle is always charged and ready to drive.


  • Is completely waterproof
  • Features strong vibration protection
  • Doesn’t cause a drop in voltage
  • Powered at 12 V
  • Easily charges two battery systems
  • Is backed by a 12-month warranty


  • Doesn’t work well with newer computer charging systems

JayCorp Smart Dual Battery 140A Isolator

The compact size of this battery relay isolator ensures that it can be easily installed anywhere. Because it features an easy three-wire connection, users don’t have to worry about bypassing the current wiring in their systems. Additionally, it doesn’t experience a voltage drop when used, which means that your vehicle will continue to operate normally.


  • Easily senses both batteries and can charge either one
  • Is water- and dust-proof
  • Shows when it’s sending the correct voltage
  • Ensures that the first battery is charged before charging the second
  • Disengages when the voltage falls below 12.9 V


  • Lower operating temperature can cause this unit to fail.
  • It tends to drain primary battery while monitoring voltage.
  • Vague instructions make installing the isolator difficult.

Cole Hersee 48120 Battery Isolator

This is a very basic battery isolator that has a 140A max. The lower price of this unit is due in part to the fact that there is no middleman involved in shipping or marketing it, which means that customers can contact the company directly when they have any problems. It’s possible to connect two batteries in parallel to charge from this unit.


  • Includes one-year warranty
  • Has 12 V DC input and output volts
  • Is built to meet OEM specs
  • Has very small voltage drop
  • Is easy to measure diode drop


  • It’s easy to crank down on the terminals during installation and damage the unit.
  • Mounting tabs are awkward and make it difficult to use a wrench during installation.
  • It can tend to drain the battery when not installed correctly.

WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator

This fully automatic battery isolator is great for use with any vehicle that has an auxiliary battery. It’s smaller than other options on the market and uses electronic switching control technology to ensure fast and even charging. Thanks to the reset/override button, users can easily switch to parallel mode when they need to jump start their vehicles. The surge protection on this unit ensures that vehicles won’t be damaged and protects batteries.


  • Is suitable for marine use
  • Automatically charges auxiliary battery
  • Features manual override to start battery
  • Offers surge protection for electronic systems
  • Includes mounting bracket
  • Is relatively easy to install


  • It can run down batteries if the vehicle isn’t regularly cranked.
  • Some users have reported the unit breaking easily during installation.
  • It doesn’t always stay in place once mounted.

True UTV-SBI-CM UTV Dual Battery Connect & Monitor Kit

Users never have to worry about being stranded when they opt for this powerful battery isolator. Because it is not only easy to install but also will quickly draw power from alternate batteries to keep a vehicle running smoothly, it won’t fail once it is installed correctly. It works well in all conditions, even when soaked in mud or water, making it ideal for marine applications and for use on off-roading vehicles.


  • It comes with all necessary installation components, including wires.
  • Included gauges make it easy to check the condition of the unit and battery power.
  • Clear instructions make installation easy.
  • It will quickly draw power from the second battery if there is a problem with the first.


  • Some users report not having enough wire for installation.
  • The mounting holes are a little small.
  • The wiring diagram can be misleading for some users.

For more guides and tips see these articles:

I think that the WirthCo 20090 Battery Doctor is the best battery isolator on this list. It is a 75 amp/100 amp isolator that makes it easy to start your battery and is always charging your auxiliary battery for you. This means that you never have to worry about your RV battery failing you when you’re on the road. Thanks to the advanced surge protection, your electronics and other appliances that are plugged in won’t be in danger even if there is a surge from the battery. I think that everyone should consider this option to ensure that his or her auxiliary battery is always charged and that the isolator won’t be damaged by bad weather.

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