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Battery isolators vs. separators: Same, but different

We’ve all experienced that annoying situation where we face battery drains because of the electrical accessories in our car, and we want to fix the problem by getting multiple batteries. But, unfortunately, when we get extra batteries for the vehicle, the auxiliary battery starts draining the power from your car’s main battery.

In such circumstances, separators and isolators play a significant role in saving your life (well, not literally!). But before you get one of these, there are some essential things you need to know about each of them.

So, let me brief you about what isolators and separators are, what purposes they serve, and which one you should get.

They both help against parasitic loads (Battery drain)

If you don’t know what parasitic loads are, the term refers to any electrical appliances and applications that demand extra power from the engine. It refers to all the power that any car consumes, even when the engine is off. Many RVs suffer from this problem where the battery drains because of the standby gadgets, devices, and electrical tools inside the vehicle. Ironically, as cars evolve and become more modern with time, these electrical loads are becoming more prevalent. Entertainment systems, audio, video players, and fancy lights only add to the incidence of parasitic loads.

Battery isolators and separators help with this problem. The most important and memorable similarity between them is that they help manage your vehicle’s multiple batteries. As a result, they minimize the chances of your battery being drained by various electrical accessories and applications in your car. This way, they reduce the chances of you having to replace your car battery very frequently, face ongoing issues because of it, or be late to work because your car won’t start one morning!

But even though the two are significantly similar in terms of their benefits and function, they work pretty differently.


Initiating the comparison between isolators and separators, let us first discuss isolators in detail. Then, after you figure out how it works and what advantages and drawbacks it offers, you can make a better, quicker decision about whether you would prefer having it.

How isolators work

Isolators can be described as distributors in automotive electrical systems, meaning that their primary purpose is to distribute charges. To elaborate, isolators have diodes, ensuring an evenly distributed charge from an alternator among all the various batteries in your vehicle. Most electrical systems with audio setups require a minimum of two batteries to operate and function properly. One of these batteries is a primary one responsible for starting your vehicle and running factory accessories. The second battery is usually accountable for powering the amplifier.

The most significant issue with having multiple batteries in your vehicle is that when fully charged batteries are connected to dead or partially charged batteries, they can create problems. This process of parasitic drain continues until you install an isolator. An isolator evenly distributes the charging current from the alternator between both the batteries. This way, each receives all the charges it needs depending on how much it is currently charging.

Moreover, isolators use their diodes to ensure that the current originating from your alternator moves in a single direction only. This way, it eliminates the possibility of the current leaving one battery for another. Plus, it prevents any other loads in your charging system from draining your vehicle’s primary battery. Hence, the isolator literally isolates each battery and makes it a fully independent and available power source. Thus, it enables primary batteries to save their charge and use it to start the vehicle and run factory accessories, which is its primary job.

Pros & Cons


  • Ensures correct distribution of power charge
  • Enables a safe second battery recharge
  • Performs as an adequate dual battery relay
  • Allows you to use your electrical devices and accessories


  • Diode isolators have a large heat sink
  • If the isolator is somehow compromised, your entire battery system is toasted


Moving on, in comparison to isolators, let’s talk about separators now. Despite being in the same niche and category and having significant similarities with an isolator, a separator has distinctive features.

How separators work 

Separators are often regarded as switches that could potentially direct currents. Technically, they allow auxiliary and primary batteries to use solenoids and charge from a single source. Battery separators use the phenomenon of prioritized charging, meaning that they will charge the car’s primary battery and then move onto the auxiliary battery. Separators monitor both your battery’s voltages. And, if it spots inadequate voltage anywhere, it activates the solenoid and allows a flow of current from one auxiliary battery to another and level the voltage. 

During this process, if your system’s voltage falls below a particular threshold, the separator automatically disconnects the battery banks from one another. This way, it protects the batteries from draining excessively. Moreover, separators also help in starting engines when a primary battery does not have enough charge. As the separator notices that the primary battery has a low voltage, it automatically opens the bank of the auxiliary battery to help start the vehicle. It enables the current to move in various directions. This way, an auxiliary battery can successfully charge others in the same charging system.

Pros & Cons


  • Creates physical barriers between positive and negative electrodes
  • Plays a vital role in providing safety for lithium-ion batteries
  • Shutdown when temperatures move above the melting point
  • Stops the iron movement between the cathode and anode and prevents thermal runaway


  • Separators do not offer protection from parasitic draw like isolators
  • Batteries can potentially be drained if you don’t monitor them
  • Not as flexible as isolators

The Key Difference 

Despite all the elaborate comparisons we have done above, the critical difference between an isolator and a separator is that they have a different current flow: 

The current flow refers to how each of these battery tools allows the charge to move in. Both isolators and separators have the same responsibility of managing the charge. However, both of them will enable the power to move in different directions.

Isolators function using a diode system which only allows current to flow in one direction. In contrast, separators use a solenoid to maneuver the power and choose which source they want to use. This difference is the most important one and makes each of these devices ideal for a unique purpose. And so, regardless of how similar the two are, they’re used differently, which leads us to our next point of discussion: which one should you use?

Which One You Should Use 

Since isolators and separators are ideal for different purposes and use, it can be hard to decide which one you should get. However, making that decision is relatively more straightforward if you know your particular requirements and preferences. The following are two of the most prevalent circumstances that car owners are in. Depending on which category is yours, you can make the right decision.

If you are ysing a system with multiple batteries

In this scenario, you should choose an isolator. Isolators are particularly recommended for engines that are frequently started and stopped. If you have a utility vehicle that you use pretty often and turn it on and off repeatedly during the day, you should use an isolator for it. 

While we’re still on the subject, here is a popular recommendation if you choose to get an isolator after all: Stinger SGP 32 200 AMP battery isolator:

Stinger SGP32 200 AMP Battery Relay Isolator
Stinger SGP32 200 AMP Battery Relay Isolator
It prevents the discharge of the primary battery, extends the overall battery lifespan, and allows an adequate current transfer. All in all, an isolator is an excellent choice if you own an RV.

If you need a reliable backup system with one auxiliary battery (Where some parasitic load is still acceptable)

In a different case, if you intend to use the batteries in parallel or when you want to charge them very quickly, separators can be a practical choice. For example, they are usually popular in dual battery systems, like trucks equipped with a plow. And if you decide to get a separator for your vehicle, here is an excellent option to go for: Bussmann RB-BS-1314 100 AMP battery separator. 

Bussmann RB-BS-1314 100 Amp Uni-Directional Battery Separator
Bussmann RB-BS-1314 100 Amp Uni-Directional Battery Separator
It has a unidirectional flow with a solenoid, providing a priority charging system for all multi-battery vehicles. It is ideal for alternators, primary batteries, and auxiliary battery systems of around 100 AMPS.

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