Dual Battery System: A Beginner’s Guide. Agm battery isolator

How Does a Dual Battery Isolator Work? – The Ultimate Guide

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So, how does a dual battery isolator work? The workflow is pretty simple if you follow this ultimate guide till the end.

An isolator has a strong relationship with the battery. Large trucks, airplanes, boats, utility vehicles, and recreational vehicles frequently use battery isolators. However, the use of another battery would be a good idea to ensure backup. That is where a dual battery isolator will come in handy.

Most types of vehicles run on battery isolators. So, it is important to know how a dual battery isolator works. Keeping that in mind, we gathered ideas to demonstrate the workflow of a dual battery isolator in the best way possible.

What is a Dual Battery Isolator?

An isolator is a mechanical switch that separates the input and output of a vehicle or device while it is connected to a battery. A dual battery isolator is pretty similar, except there are 2 batteries instead of one.

Being a two-port device, an isolator can only transmit frequencies (radio or microwave) in a single direction. Its internal characteristics function in a way that allows propagation from one direction while blocking the other.

The first one is the Starter battery, and the second one works like an Accessory battery.

How Does A Dual Battery Isolator Work: Explained In Detail

As we previously mentioned, multi or dual battery isolators are used in aircraft, large trucks, boats, and other utility vehicles that need to use multiple batteries as source of backup power. Nowadays, isolators are also used in functioning electric vehicle systems. We believe its use will only increase in the future.

-So, it is important to know the functionality of a dual battery isolator.

A dual battery isolator works closely with an electrical battery, permitting electricity or frequencies in a single direction. At the same time, it prohibits electricity from flowing from the opposite direction.

What does a dual battery isolator do?

The primary purpose of a dual battery isolator is to keep the entire electrical system running even when the primary battery dies. This is the reason why this kind of isolator is frequently employed when you need multiple batteries.

A multiple battery isolator, or specifically a dual battery isolator, can help your vehicle go further when you use it as a solenoid priority system in a battery. This is how it extends the life of your vehicle’s battery. As a result, a dual battery isolator backs up the battery with a charge so that it can stay out longer.

Why Should You Use a Dual Battery Isolator?

If you have gone through how a dual battery isolator works, then you can guess why you should need one. Most of the time, people need dual battery isolators to power airplanes, boats, trucks, recreational vehicles, and utility vehicles.

But why not single battery isolators, right?

Well, these types of vehicles need dual battery isolators because one battery starts and runs the engine, whereas the other one loads accessories like radars, winches, and other instruments. The isolator powers the starting battery. At the same time, it prevents the secondary battery from failing or draining due to excessive load.

Day by day, electric vehicles are also now leaning towards using isolators. Off-road vehicles require a dual battery isolator to handle high current loads, like a recovery winch. Additionally, you will need to use a dual battery isolator to power large, powerful stereos in vehicles.

Pro Tip – When you are ready to use the battery isolator, make sure you know how to test a battery isolator. In case, you don’t know the way to test your car battery isolator, you can check our other guides.

Benefits of Using a Dual Battery Isolator

A dual battery isolator benefits you by connecting two batteries together. So, the relatively weak battery can get charged from the strong one. It is like a backup for the whole system and for the primary battery.

Drawbacks of Using a Dual Battery Isolator

Well, there are a few disadvantages to using a dual battery isolator. We have listed down a few –

  • It is always costly to use a dual battery isolator.
  • The setup process of a dual battery isolator is not simple.
  • While using the common diode-type isolators, an extra drop in voltage will be applied to the circuit. It will occur in the middle of the batteries and the charging source.

The Dual Battery Isolator Setup: Things to Take into Account

There are a few things to look at when you are going to set up a traditional dual battery isolator. This type of setup is relatively less expensive than other types of setups. On top of that, it is very flexible.

Let’s take a look at the considerations of a dual battery isolator setup –


The size entirely depends on the type of vehicle. For instance, some pickup trucks come with a default location in the engine bay for installing the secondary battery. But that is not always the case.

It can be difficult to install a large 105 AMP lead acid battery when there is no dedicated space in the engine bay. As a result, check battery dimensions after determining the AMP.


Most of the time, it is better to keep the charge of a lead acid AGM battery below 50%. That is when it offers the best performance. Although it is not exactly recommended, it can enhance the lifespan of the battery and help it avoid damage.

Considering that a 75 AMP battery will perform for 37.5 AMP hours at 450 watts while it is charged below 50%.

Aside from that, not all vehicles contain the same battery. Then again, various batteries have various requirements in terms of amperage and voltage. Usually, the better isolators on the market drain 100 AMP to 150 AMP at regular wattage.


In addition to the AMP, voltage is another important factor to look at. Due to voltage inconstancy, some electronics can be damaged at the time when the engine starts cranking. Therefore, determine the right amount of voltage that matches the battery’s AMP.

An easy solution to this problem would be to use a kit such as the Blue Sea System. It can efficiently charge both batteries simultaneously. In addition to that, it is far superior to a single battery isolator.


The weight of the battery is another crucial consideration. Bulky batteries like AGM, Lead-acid, or gel batteries often weigh a lot. For example, the weight of a 105 AMP AGM battery is around 70 lbs. Additional weight can make your vehicle heavy and require more power to run.

You can go for the pricier options, like the new lithium battery. In comparison with typical batteries, it offers more power yet weighs less than half.


You sure don’t want to mess up the electrical system of your vehicle with the wrong battery isolator. importantly, choosing the incorrect detector might cause more problems than you expected. That is why you need to ensure which type of battery isolator is perfect for your vehicle. Luckily, picking a reliable battery isolator is not that difficult.


A dual battery isolator system is not easy to set up. It requires a significant amount of space in your car to organize all the wires and other components. Considering the complexity of the installation process, some people think of integrating a solar generator instead of an isolator.


Last but not least, you need to think about the total cost of setting up a dual battery isolator. Buying all the components may require a substantial amount of money. But it is not that much.

Here is a summary of the total cost to set up a dual battery isolator in a Toyota Sunrader. Take a look to get an idea for your vehicle –

  • 80 for an isolator.
  • 130 x 2 = 360 for dual 150 AMP lead-acid batteries.
  • 300 for a 1000 watt inverter.
  • 120 for 25 feet of DC wiring (2 to 4 gauge).
  • 860 in total.

For extra power security, you can purchase a 100 watt panel and a solar charger for around 250. But that is up to you.

After setting up a dual battery isolator in your vehicle, it is time to judge whether it is performing as you expected or not. The best dual battery isolator should show the following symptoms.

Build Quality

Often, you should look for components like studs in an isolator, which contact electricity. These studs should be made of copper and plated with tin. Also, this makes the components corrosion-resistant and optimizes their conductivities.

A weatherproof chassis with a renowned certification like IP67 can increase the rigidity of the components to the next level. Such isolators can withstand temporary submersion up to a few feet.

Other Considerations

Basically, the above are the crucial things that you need to keep in mind when choosing a dual battery isolator. However, there are some other considerations that may help you a bit further in making the right decision.

  • For instance, it is better to send a couple of bucks for a 120 AMP DC unit than a 65 AMP. Having room to grow is always a plus.
  • A dual circuit battery from the E-series can withstand a lot of abuse. But after a decade of consistent use, it is better to replace it.

Types of Battery Isolators

Judging by the schematics, we can divide a dual battery isolator into three types. Without further ado, let’s take a look at the dual isolator battery types –

Diode Battery Isolator

The semiconductor diodes in the Diode Battery Isolator divide the current coming from the generator or alternator so that two or more batteries can be charged simultaneously. It is the regular type of dual battery isolator where one battery charges the engine to start, and the other run other accessories.

Luckily, the secondary battery for running the accessories doesn’t drain the primary battery. As a result, it can run the engine for a long time.

Battery Solenoid Isolator

The auxiliary battery is always connected to a solenoid in the Battery Solenoid Isolator. The solenoid remains active during times like starting or charging the engine and other components. Then, it gets disconnected from the auxiliary battery when it is not in use.

Users can switch the solenoid at all times, when the engine is off, or at the time of ignition. It depends on the usage. However, following some DIY, you can start a car with a bad ignition switch.

Battery Switch Isolator

In a Battery Switch Isolator, semiconductor diodes divide the current coming from the generator or alternator. It is able to charge more than two batteries at the same time.

Just like a Diode Battery Isolator, one battery powers the engine, and the other one powers the components. Also, the auxiliary battery doesn’t drain the primary one. As a result, the main battery receives a sufficient charge to run the engine continuously.

A Battle Among Three Types of Dual Battery Isolators

Below, we have drawn a comparison chart to show the differences among the three types of dual battery isolators –

Diode Battery Isolator Battery Switch Isolator Battery Solenoid Isolator
It doesn’t require a separate ignition to start. It requires a separate ignition from the wiring to start. It depends on the solenoid and how it is switched.
Installation is a challenge. Installation is complex, but not like a Diode Battery Isolator. It’s relatively easier than the other two.
It requires changing the wires manually. It requires changing the batteries manually. It doesn’t require much change.
It runs on one condition. It also runs on one condition. It runs on the three conditions of the solenoid switching.

Can a battery isolator drain a battery?

No, it’s the opposite. A battery isolator can prevent batteries from draining each other, but it cannot drain a battery on its own. If you are worried about your battery voltage dropping while you’re driving, the reason is not your isolator. A battery isolator works as an electrical bridge between multiple batteries. In doing so, it ensures that all batteries receive the same amount of energy while preventing any one battery from being drained by another attached to the isolator.

How Does a Dual Battery Isolator Work? — Final Words

We are now at the end of this article. So, we are going to ask – have you understood the procedure of a dual battery isolator? We expect the answer is yes. It has been a broad discussion of everything about a dual battery isolator.

Regardless of the type of your vehicle, it is always better to install a dual battery isolator rather than a single one. On the other hand, a multi-battery isolator is larger than what any vehicle may actually need. Leave a comment if you have any questions regarding a dual battery isolator.

A versatile content writer – mainly an expert in the car the camera niche. He has been writing since 2016 for many car and camera blogs. He loves to discover new things and write them to guide people.

The ultimate guide to dual battery systems

If you need your rig to power gear such as a portable fridge, safety lights, or radios while your fourby is parked, you’re going to need a dual battery system.

Don’t run the risk of losing power to your gear, and ensure your vehicle is always ready to start up with the installation of a 4WD dual battery system.

What is a Dual Battery System?

A dual battery system is a vehicle battery system that uses a secondary battery in addition to a vehicle’s starter battery. This secondary battery is used as a power source to auxiliary gear and accessories.

How Does Dual Battery System Work?

In a dual battery system, both batteries function as two isolated systems. While your vehicle’s engine is running, your starter battery works with your alternator to power your vehicle and its electronics.

While your vehicle is turned off, your secondary battery powers all gear and accessories attached to your vehicle; meaning that you can run your portable fridge, lights, and inverters without having to keep your engine running.

This is achieved thanks to the function of an isolator that disconnects your starter battery from your secondary battery, meaning that you only draw power from one battery at a time.

Keeping each battery functioning independent of each other is crucial in ensuring that your starter battery does not become drained and prevent your fourby from starting up. The battery isolator will also ensure that both batteries charge properly.

Be aware that some 4×4 dual battery isolators can allow your starter and secondary batteries to work together, boosting starting power to your vehicle should the starting battery suddenly drop in voltage. This is not the case with all isolators, however.

Your auxiliary battery will most likely be a deep cycle battery. This is because deep cycle batteries are built to be repeatedly discharged and recharged without being damaged or shortening their lifespan.

By using a deep cycle battery to power your gear you can rest easy knowing you’ll have a consistent power supply and won’t risk damaging your battery by running it dry.

The Pros and Cons of Installing a Dual Battery System

If you’re unsure if a dual battery system is right for you, consider these pros and cons.


  • Allows your rig to power a fridge, radio, lights, inverters, and whatever else you need while you have the ignition off.
  • No need for concern in draining your starter battery.
  • Increases power available if you need to use your winch.
  • Able to charge your secondary battery with solar panels.
  • Peace of mind in case of primary battery failure.


  • Added weight to your rig due to an extra battery box.
  • The potential cost might be too high if you’re on a tight budget.

What is the Best Dual Battery System for Me?

No two rigs are the same, nor are two 4WD enthusiasts. Thankfully, the experts at Total 4×4 have over 30 years of experience and can help you pick the best dual battery system for your 4WD.

We highly recommend gear made by TJM and REDARC. Both Australian born and bred, these manufacturers provide all the electronic components needed for a dual battery system setup. The REDARC Battery Isolator is a Smart isolator that is an easy recommendation for those of you thinking of installing your first dual battery system.

Whether you’re upgrading your dual battery system or installing one for the first time, TJM and REDARC are excellent choices and leaders in the market with good dual battery systems reviews from 4WD owners.

Once you have the rest of your battery kit, it’s time to choose a secondary battery.

Types of auxiliary batteries

Lead Deep Cycle

Suitable under the bonnet, or in an open tray or tub. Cheap, but are known to suffer from a reduced lifespan if not fully discharged and recharged each use.


The popular choice among any rig, AGM batteries are suitable anywhere as they do not let out any hazardous gases while charging. This type of battery is better suited to partial use and recharge, rather than fully discharging and recharging in a use cycle.


Boasting reduced weight and increased capacity, lithium batteries are the most durable battery when used in a partial use cycle. However, due to heat restrictions these cannot be fitted under the bonnet of a vehicle.

Installation Basics

If you’re considering installing your dual battery system yourself, have a look at our brief step-by-step guide to see if you’re up to the task.

  • Mount the second battery on your rig, ensuring you have enough wire to make the necessary connections to your second battery.
  • Disconnect your starter battery.
  • Mount the Voltage Sensitive Relay (VSR). Place the VSR close to the main battery and away from any hot or moving parts.
  • Cut cables to length.
  • Fit lugs to the bare ends of cable by stripping away 15mm of insulation and crimping them in place. Slide the heat shrink over the lug and apply heat to provide a waterproof seal.
  • Use the black wire attached to the VSR to earth the relay.
  • Connect the main battery to the VSR.
  • Earth your second battery.
  • Attach the VSR to the mounting plate. Positive cables may not be attached to both batteries.
  • Attach the negative leads, first to the starter battery and then to the second battery.
  • Test your system is working with a multimeter.

At Total 4×4 we offer a DIY 4×4 Dual Battery System Kit to give you everything you need to get started including a comprehensive installation guide.

How to Keep Your System Running Smoothly

Like any component in your vehicle, your 4×4 dual battery system will suffer from wear and tear, especially if you’re heading off-road and facing the elements.

To keep your charging system running smoothly, regular maintenance is required.

Before you head out, check your system for any damage to the battery, DC charger, wires, and battery tray. Keeping your system in good condition is the best way to keep things running smoothly.

dual, battery, system, guide, isolator

If you want to know more about the best dual battery systems or dual battery system prices, don’t hesitate to get in touch with the experts at Total 4×4 to see how we can improve your rig today.

How To Install A Battery Isolator In Your Conversion Van

Battery isolator systems allow you to charge the secondary batteries in your van when the motor is running.

There are many variations of hooking a system up, but they all e common goal: to “isolate” your secondary battery so that when you’re running all of your electronics you don’t drain the starter battery.

Why You Should Have A Battery Isolator?

First off, battery isolators are relatively cheap to install. For less than 150, you can tap into as much power as you would get from 1000 of solar.

Secondly, they compliment solar systems really well. If it’s cloudy for a few days and you need some juice to charge your laptop, all it takes is a drive to the grocery store or your next campsite to get a little boost in power.

In a van, you’ll likely be traveling around, and it’s great to make use of the already running motor and vehicle electrical system.

If you’re on a strict budget and just need a small battery for cell phones and some lights, an Isolator and battery might be the only thing you need to get you started, and you can add solar when you get some more cash.

How To Pair An Isolator With Solar

The good news is that you don’t need to do anything special here! You can install this system right alongside your solar system.

Both the alternator in your vehicle and your solar charge controller are Smart devices that monitor battery voltage and adjust their current to make sure that your battery doesn’t get overcharged.

What A Battery Isolator Cannot Do

A battery isolator only transfers power from the alternator to a secondary battery. The van’s alternator is designed to keep a float charge (13.8V) on a starter battery as well as provide enough power to keep all of the van’s equipment running, such as lights and a stereo.

It’s a great, simple device for this, but it’s not meant to charge up a secondary battery from deep discharge.

This means that the 13.8V charge is enough to get your secondary battery charged most of the way, but because it will never see a full multi-stage charge cycle (at points needing to be in the 14.5V range), it will never completely charge your secondary battery.

For many van dwellers, this isn’t a huge issue. All it means is that your batteries will wear out quicker and lose capacity over time. You may need to replace an AGM or FLA battery after 2 years rather than 4-5 years.

For smaller systems, this is a relatively small cost. The cost of a proper B2B charger might be more than you’re willing to spend on a small campervan battery that you only plan on using for a summer or two.

Also note that most MPPT charge controllers do use a multi-stage charge, so if you’re getting a lot of sun, you may not need a full charge cycle from your alternator and you can just use it to boost the system while you’re driving.

For those camping for long periods of time without driving, this may be an optimum approach.

How To Install A Battery Isolator

As we said, there are a couple of different ways of hooking up your secondary battery. The general setup is similar for each option.

First check out the infographic below for the basic install layout, and then read on about the different ways isolate your batteries.

The install is one of the more basic things you can do for your electrical system. You need to find a space in your engine bay near the batteries to install the isolator and make sure you properly crimp the terminals because you’re dealing with heavy gauge wire.

Parts Needed To Install A Battery IsolatorNotesQuantity
Ring Terminals Use a 4 AWG and pick out a ring eye size for the isolator you buy. 4-6
Heat Shrink Useful for all wiring installs 1
4 AWG Fuse Holder Install on both ends close to the battery to protect as much wiring as possible 2
Isolator See below for options 1
4AWG Stranded Battery Wire Use stranded wire for better routing and stronger connections 25-50 ft (varies per van)
Manual Cutoff Switch (Optional) 1
Secondary Battery Ground Cable Completes circuit for alternator charging 1

Which Type Of Battery Isolator To Install:

There are four basic ways to make a connection to the secondary batteries. Each have their pros and cons, so pick one that fits your needs.

  • Manual Switch
  • Basic Relay
  • Voltage Sensitive Relay (VSR)
  • Diode Based Isolator

Manual Switch

A manual switch can be paired with the other systems so that you have a hard disconnect as an extra step of safety for working on the leisure batteries.

Manual switches are the most “risky” because you have to remember to turn them off when you stop the van. You only need to forget once and you can accidentally drain your starter battery to strand yourself.

Best Use: if you are on a severely limited budget and want the simplest way to charge your batteries but plan on upgrading later.

Pros Cons
Inexpensive Not automatic; you can drain your starter battery if you forget to turn it off.
Simple; fewer parts to break
Can use secondary batteries to start the car if the starter battery is dead
No voltage drop

Basic Relay

Relays are mechanical switches that use an electrical “signal” to turn on. They use a little bit of electricity – in this case a 5A wire- to make a connection that much more amperage can travel through- such as a 120A alternator.

The relay signal wire physically moves a piece of metal in the relay to connect the large wire going in to a wire going out. Because it’s a physical connection, there is no voltage drop as a result.

There are moving pieces in a relay, and they can fail. Because of the high amperage connection, the connection can “arc”, which welds the contacts together.

This permanently connects your starter battery with your secondary battery without you knowing. If you happen to drain your batteries, it can leave you stranded. This doesn’t happen often, but it’s good to be aware of.

This is the most complicated of the options to install because you have to wire in a signal to the relay.

For battery isolation, you want your relay to activate when the van is running. The best way to do this is to find the “accessory” wire in your fuse box and tap into that wire.

Many times this takes some trial and error with a digital multi-meter to see which wires read 12V when the van is on, but 0V when it’s off.

Optionally: you can add a toggle switch to the cab area so that you can turn the relay off in the even that you want to. At the least it adds to the cool factor!

With this system as long as your starter battery has a little charge to activate the signal wire, you can use your leisure batteries to help jump start the van if it dies. This doesn’t happen often, but is a nice backup for those people who plan on being far away from civilization.

Best Use: You have some experience with electronics and don’t mind troubleshooting complexity if it would arise. It is a more budget-conscious option while still protecting your starter battery from accidentally draining.

Pros Cons
Relatively inexpensive complicated to install
Replacement can usually be found at automotive stores Relay has moving parts; more things to break from use / vibration
Can be used to start the van if the starter battery is dead If the event you leave your ignition key “on” with the van not running, you can drain the starter battery. Unlikely, but it’s possible!
No voltage drop

VSR (Voltage Sensitive Relay)

A Voltage Sensitive Relay (VSR) is an automatic component that activates when it sees that higher voltage from alternator charging and then turns off when the voltage drops.

This is a clever way to not need any external signal wiring so it is easy to set up.

Because it is relay based, it has the same downfalls as the simple relay above. One of the failure modes can leave your batteries permanently connected, which leaves you unable to start your vehicle if you drain the batteries all the way.

The only way to know that this has happened before it causes problems is to have a voltage reading of your starter battery and secondary battery and keep track of them. If the starter batterie’s voltage stays the same as your secondary battery, the two are connected.

Because the alternator needs to be running for a VSR to work, if your starter battery is dead, there is no direct way to use the leisure batteries to help start the van. There is a relatively small risk of needing to do this anyway if your starter battery is healthy.

Best Use: You want the easiest way to get alternator power in a set-and-forget system. With no voltage drop, this will be the go-to option for most camper vans.

Pros Cons
Easy to install Relay has moving parts; more things to break from use/vibration
Set and forget Can’t use the secondary batteries to start the van if the starter battery is dead
No voltage drop Can’t disconnect when the motor is running

Diode Based Isolator

Diode based isolators are the tried-and-true system for electricians. They use electrical magic to charge starter battery and after it is fully charged they divert power to the leisure batteries.

There is no way for power to flow between your two battery systems so you can’t accidentally drain the starter battery.

This type of Isolator installation is slightly different from the other options. The Isolator is wired in between the alternator and the starter battery. For some newer vehicles, a simple isolator creates problems with the electrical system. In this case, a 4-post isolator can be used although they are about twice as expensive. See the install instructions on Littlefuse.com for more info.

The linked isolator is fully sealed in epoxy with large cooling fins to reduce the strain on the electronics. There are no moving parts to break and because it is fully sealed it is water and dust resistant.

Best Use: You want the most robust option available and are willing to trade a little voltage drop in exchange. This is our favorite system, and while diodes can wear out, they are the best combination of simplicity and durability if you’re willing to install it properly.

Pros Cons
Easy to install Diodes system has a voltage drop
Set and forget Can’t use the secondary batteries to start the van if the starter battery is dead
No moving parts: most durable option Can’t disconnect when the motor is running
Separated battery banks is ideal for avoiding potential balancing issues expensive

Kate Moore

Kate is the lead content creator for ParkedInParadise.com and has spent over two years living in a camper van conversion. She has traveled through 48 US states and writes about van life, camping and RV living.

This Post Has 24 Комментарии и мнения владельцев

Hi, love your website, I have recently purchased the True brand vsr as it is featured in another web site, reading the product info on Amazon it states that this unit will engage the starting battery / house battery if the house battery is being charged by solar/battery charger and the start battery is low, am I wrong?

dual, battery, system, guide, isolator

Nope-not wrong: that’s the way it should work. The VSR will connect the two batteries (house and starting) once the system voltage gets high enough to indicate that they’re charging. This can happen from the charge controller end or the alternator end. It will then disconnect the two batteries once charging voltage drops. Most of the time your starter battery will be fully charged after a short drive so it doesn’t usually need charge, but in certain circumstances it can.

What is most confusing is the cutoff switch. If I run the wire from the isolator to one of the lugs on the cutoff switch, then to the aux battery, what do I do with the other lug on the cut off switch? Does it get grounded or does it get connected to the negative side of the battery?

I believe you’d run the wire from the isolator to one of the lugs on the cutoff switch, then run a wire from the other lug on the switch to the aux battery. Leaving the switch open, or on, will allow the alternator to charge the aux battery through the isolator. Closing it will shut this function off. I can’t imagine a situation where you’d need to turn this switch off, as the isolator will keep the two batteries, well, isolated. It’s more of a secondary, backup cutoff. I’m about to run this setup and I’m electing not to use a manual cutoff switch, as it is not necessary IMO.

Is it possible to use VSR with GEL batteries? Since the chemical content of GEL batteries very sensitive to the suddenhigh current I really suspected to use it.

If you’re using the Basic Relay – would it matter that there are two different type of batteries? For example, we have a Lithium house battery and a lead acid car battery – is it okay to use the basic relay between the two? Are there any downsides?

Hi, and thank you for this forum. I want to run a small fridge off my second battery, which is going to be charged by a Smart battery isolator. So the solar controller and the isolator can both be delivering charge to the second battery while that second battery is running the fridge? What is the best way to do the connections at the battery? Do I simply “stack” the connectors on the battery posts? Thanks.

The 4 Gauge wire that you have posted above has many 1 star reviews claiming that it is actually 6.5 gauge wire. You might want to update that link so that people using your links will purchase the right size wire.

First, great site! Thanks for all the insight. I just installed my battery isolator. I’m noticing my wires are getting hot near the inline fuses. Let me know if you have any suggestions as to why.

I don’t know if you got the problem fixed. If not let me know and I can explain why the wires are getting hot. It is a simple fix. Or look up the big 3 upgrade it will also tell you.

Thanks for the very informative post! Space is very tight in my engine bay (2010 Odyssey), and there really isn’t anywhere to install my battery isolator. I’m wondering if there’s any reason that the isolator has to be physically near the starting battery-could I install it near the house battery in the rear of the van instead? The isolator is a Key lime Iso-Pro140, if that’s important.

Hey, looking to install a simple manual set up – looking at the wiring diagram – would i not need an inverter between the manual switch and leisure battery ? What side would the fuse go if this was the case ? – how would i add a battery level indicator to read the 12v lesuire battery ? Thanks – best website ive found regarding battery install

The VSR isolator kit I bought came with 20 feet of 7AWG wiring. I will probably need to use at least 10 feet of that. Will there be a significant voltage drop if I use the 7 AWG? Should I just go ahead and buy some bigger wire?

I’ve got a problem you might understand. I want to use the VSR solution as shown above. Given its labeling, it outputs 12V up to 140A. My battery has a maximum input current of 50A. What do I do to make sure that the current coming from the battery stays underneath 50A? I understand the circuit breaker will activate if the rated amps are exceeded, but I don’t want to plan on that happening! Is there a way to limit the amps coming from the VSR?

Hi, did you ever figure out an answer to your question? I’m wondering the same thing. Thank you very much!

hi, I wanna connect an inverter to charge my laptop, a coffe maker and have an extra plug, how many “A” has to be the leisure battery? do you recommend any brand of battery? Thanks

What about newer van? with Smart-alternator? i understand the VSR and the basic relay wont work with the Smart-alternator. Is there are other option then manual switch (cheap, uncomfortable) and DC-DC charger (300 too expensive)? Thanks

Hi! My current van set up is with one 12V Renogy deep cycle 100ah battery to the alternator. My question is, can I install an additional battery next to the current battery to get double the power? Can the alternator system handle that and what is best practice for that? Thank you

Ive been told I need to run another ground from my secondary back to my starting battery. Is this correct or should I be fine with grounding it directly to the chassis? Also, can I position my Smart Isolator in the rear of the van rather than under the hood? Thanks!

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How to Choose The Best Dual Battery Setup

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When we decided to turn the truck into an overland adventure vehicle, one of the most challenging elements we had to consider was a reliable way to meet our power needs while camping. Especially with our plans of working remotely while off grid.

In this post we’re going to walk you through our dual battery system decision process, the camping power supply options available, and how you can integrate a solar generator into your dual battery setup to meet your camping power needs.

DISCLAIMER: We are NOT professional electricians. The information provided in this post is bore solely from our personal experience and opinion. A professional should always be consulted when dealing with any electrical system

Assess Your Needs For a Dual Battery Setup

First, if you’re completely new to electrical systems, start by checking out Part 1 of our Camping Power Series for a straight-forward explanation of basic electrical terms and principles.

Next you’ll want to narrow down all the electrical devices you may need to power while camping or traveling using a dual battery system.

For us that list looked fairly simple at first glance:

  • A 12v Camping Fridge
  • Charging Mobile Devices (2 cell phones, and a laptop)
  • A Vent Fan
  • Lighting for our truck camper

Then you will need to determine the power consumption (watt usage) of each of those devices from a day-to-day perspective based on your usage. BEFORE you can make an informed choice on a camping power supply or a dual battery system that’s right for you. especially if you’re planning to camp off-grid for any length of time.

A watt meter. which is a device that measures power usage/draw. is very handy for determining the power consumption of your devices, OR you can look at the device’s power supply label and use the below formula to get a fairly decent idea:

Watt Need = hrs of usage per day x amps per hr drawn by the device x volts

Check out Part 2 of our Camping Power Series for a more detailed explanation of how to calculate your camping power needs, to help estimate the type of dual battery setup you’ll need (it includes a free downloadable camping power needs calculator).

You may require more or less power than our own personal dual battery system depending on how many devices you need to power and how much you use those devices while camping. Just keep in mind:

The more devices you bring camping, the more power you’ll need.

And the more power you need, the more expensive your dual battery setup will become.

Consider Your Dual Battery Setup Budget

Cost is an important factor in all our decisions. And we’re sure it is for you as well! So now that you know your power needs, you can assess your dual battery system budget based on these needs.

Option 1: Single Battery SetupIf we didn’t need a fridge and a vent fan we could have gotten by using our vehicle’s existing lead acid starting battery and 12v electrical system, charging our devices from the factory 12v outlets, and forgone a dual battery system altogether.

UPDATE 2022: Since this article was originally published in 2019, there have been incredible advancements in lithium battery technology and there are now lithium dual-purpose starting/deep cycle batteries on the market that can be a viable alternative to dual battery systems, easily powering a 12v camping fridge, vent fan, etc. off a single battery while traveling. We are using one in our new overland truck build, and love it. more on this below.

Option 2: Traditional Dual Battery SetupWe could have ran a traditional dual battery setup like we had in our previous RVs, adding an additional battery that is charged separately from our vehicle’s AGM lead acid starting battery.

Option 3: Solar Generator Dual Battery SystemWhen we were downsizing from the fifth wheel, opting to build out our old Toyota pickup for budget travel, we wanted to ensure we’d never have to worry about power while camping off grid. So we splurged by integrating a solar generator into our dual battery system.

While each of these options can vary in expense depending on the specific components used, let’s walk through these options in order of average expense, so you can see which best fits your camping power needs and budget.

Select a Dual Battery Setup That Meets Your Camping Power Needs

OPTION 1. Single Battery Setup (Using your vehicle’s existing 12v Power for Camping)

Your vehicle’s electrical system consists of an alternator that charges a battery that supplies power to start and run your vehicle, as well as power 12v accessories.

  • If your needs are no greater than running a few LED lights, charging your phone(s), and the occasional laptop, your existing lead acid starting battery may be sufficient to meet your power needs while camping and you may not need a full dual battery setup.
  • By using your vehicle’s existing electrical system and a cheap inverter (we recommend a pure sine-wave inverter to protect sensitive electronics) that you can pick up from pretty much any big-box retailer or automotive store, you can simply plug the inverter into your vehicle’s 12v outlet and then plug your devices into the inverter and you’re ready to roll for a total of about 70.
  • TIP: Try to find and use devices and lighting that already operate or can be charged on 12v (car chargers). all modern phones, and even most laptops can be. But there are also some great 12v slow-cookers, ovens, and refrigerators out there.
  • Remember to assess your wattage needs, and always carry a jumper pack: Most standard lead acid starting batteries are limited to 35-75 amp hours (of which only 50% of that power is usable before the battery is dead). If you decide to run a single battery setup, you should always carry a lithium jumper pack in the event you deplete your vehicle’s starting battery while camping. If you’re not running your vehicle regularly or traveling daily, devices like 12v slow cookers, ovens, and refrigerators will likely draw more power than your vehicle’s alternator and single lead acid battery can supply. So you may need to consider a dual battery system to meet your camping power needs.

UPDATE 2022: A new 135ah (1620watt) Lithium Dual Purpose Starting and Deep Cycle Battery has been released that is a drop in replacement for your vehicle’s starting battery. We’ve been using and testing it in our latest truck build for powering EVERYTHING on our adventures, and it might be the right power solution for you as well. Read our detailed post on it here:

OPTION 2. Traditional Dual Battery Setup

In a traditional dual battery setup there is a device, called a battery isolator, that enables your vehicle’s alternator to charge both the starting battery and a second “house” battery independently of one another.

  • This is a very flexible option, and can still be done with a modest budget if needed.
  • By adding an additional battery (commonly lead-acid deep-cycle, AGM, or Gel type) for your devices’ power needs, you keep your starting battery “isolated” so that it is never at risk of being run completely dead and leaving you stranded.
  • This also enables you to add enough capacity/amp-hours/batteries to supply power for things like a crock-pot, a camping fridge, or even a microwave when combined with a properly rated power inverter.
  • Lithium Dual Battery Systems: If you’re wanting to integrate one or more 12v Lithium Deep Cycle batteries into your dual battery system, you’ll typically need to utilize a DC-to-DC charge controller, in place of the standard battery isolator, to provide safe amperage (typically 20-60 amps) for charging your lithium batteries from the vehicle’s alternator. DC-to-DC charge controllers can also be utilized with lead acid AGM batteries as a more efficient alternative to a standard battery isolator, and most DC-to-DC charge controllers allow you to seamlessly switch to solar panel charging as well.

Considerations When Planning a Traditional Dual Battery Setup

  • Weight. Lead-acid, AGM, and Gel type batteries are bulky, and often weigh a substantial amount. A 105 amp hour AGM battery, for instance, weighs almost 70 lbs! Newer lithium batteries will typically provide a comparable amount of power at less than half the weight, but the cost can be significantly higher.
  • Usable Capacity. Typically it is not recommended to discharge lead acid AGM batteries lower than 50% of their rated capacity to avoid damage or shortening their life-span. So a battery rated at 75 amp hours only has 37.5 usable amp hours (or 450 watts).
  • Size. Though some trucks have a factory location for a second battery in the engine bay, finding a place for a big 105 amp-hour lead-acid deep-cycle battery can be difficult (but not impossible).

At minimum you need a power inverter, a battery isolator, heavy gauge DC wiring (0, 2, 4, 6 ga. depending on the length and power draw) for supplying power to and from the battery isolator to your second battery, and if you want solar. a solar charge controller (or DC-to-DC charge controller) for charging your house battery, a solar panel(s), and wiring to connect it all.

  • In our old Toyota Sunrader RV we installed a traditional dual battery system that consisted of:
  • A battery isolator (80)
  • 105 amp hour lead-acid deep-cycle battery (130)
  • 1000 watt pure sine wave inverter (300)
  • About 25 ft of 2 to 4 gauge DC wiring (100)
  • We chose not to implement solar, due to cost at the time. Plus we were driving daily for hours which enabled us to always maintain a charge from the vehicle’s alternator.

OPTION 3. Solar Generator as a Dual Battery Setup

A solar generator is intended to provide an all-in-one off grid power solution for camping. They generally include a battery, solar charge controller, and power inverter, all in one compact and easy-to-use device.

They come in a variety of shapes and sizes to suit your camping power needs, and also offer lithium-ion battery options which decrease weight and size substantially. Lithium-ion batteries also have a much higher usable capacity of around 80-95% (versus the 50% usable capacity of the other battery types we discussed in a traditional dual battery setup).

However with so many solar generator options out there, and new manufacturers and models becoming available all the time, it’s hard to tell what to look for. And it’s even harder to choose what model would be best to use in a dual battery system.

Considerations When Planning a Solar Generator Dual Battery Setup

  • Usable Capacity. Typically it is not recommended to discharge lithium batteries more than 80-95% of their rated capacity (depending on chemical make-up) to avoid damage or shortening their life-span. So when a solar generator is rated at 1100 watts (or about 90 amp hrs) it actually has a usable capacity of 880 watts (or about 73 amp hours at 80%).
  • DC Charge Rate. This is very important when it comes to using a solar generator in a dual battery system for travel or camping. If it cannot charge at a fast enough rate, or worse, if it has no way to charge from a 12v DC outlet (car charger) at all. then it likely won’t be practical as a dual battery setup while car camping or truck bed camping.
  • Size. Again determine your power need (in amp-hours or watts), pick a solar generator that meets that need, then make sure the dimensions of the solar generator can fit into the physical space you’ve planned in your vehicle build, camper, etc.
  • Cost. This is the biggest caveat to integrating a solar generator in a dual battery setup. We’ve found that above a certain price point it may become more practical to go with a traditional dual battery setup. This is largely dependent on your personal needs and budget, but during our search, anything above a 1500-watt capacity began to lose justification from a cost-benefit perspective.
  • Power Output (110v AC 12v DC). The power inverter in the solar generator converts the DC power stored in the solar generator’s lithium-ion battery to AC power for devices that don’t operate on 12v DC power. Consider the devices you want/need to power, and make sure the inverter in your solar generator can accommodate the device’s power draw (e.g., if you want to use a 1000w microwave, the solar generator’s inverter needs to be rated for more than this amount). You also want to make sure the DC output of the solar generator offers a high enough amperage for your 12v devices.
  • Feature Set. Does it have enough 110v AC and 12v DC power ports? USB ports? Is it’s capacity expandable? Does the built-in LCD display monitor provide the information you need, and is it accurate? Is the battery user replaceable? Review all the solar generator’s features and make sure you’re happy with them. It’s a big investment.

When considering which solar generator model would best fit into our dual battery setup, we were able to eliminate most by taking the above considerations into account.

Updated 2022: This technology is constantly evolving and a lot has changed since we originally invested in our own solar generator dual battery system just a few years ago. Currently, the below three models (in order of cost) are the best solar generators for integrating into a dual battery system.

This is primarily because Goal Zero now offers a Yeti Link Vehicle Integration Kit which allows for much faster in-vehicle charging (300-750 watts) and is compatible with both the 1000x and 1500x recommended below. Though it does come at a steep additional cost.

Goal Zero Yeti 500X Lithium

  • Usable Capacity: 505 watt hours or 46.8 amp hours (10.8V) = appx 404 usable watts or 37.44 usable amp hours (at recommended 80% max discharge)
  • DC Charge Rate: 120 watts at 12V with factory car charger ( appx. 4.5 hours to fully recharge from dead)
  • Size: 11.25” Wide x 5.8” Tall x 7.5” Deep
  • Power Output: 300 watt continuous (1200 watt surge) Inverter putting out 2.5 Amps at 120VAC. Can output 10 Amps at 12VDC.
  • Feature Set:
  • Output Ports: 2. USB-A, 2- USB-C, 2. 120VAC, 1. 10 amp 12VDC car port, 1. 10amp 6mm 12VDC port
  • User Replaceable Battery

2. Goal Zero Yeti 1000x

  • Usable Capacity: 983 watt hours or 91 amp hours (10.8V) = appx 786 usable watts or 72.8 usable amp hours (at recommended 80% max discharge)
  • DC Charge Rate: 120 watts at 12V with factory car charger (appx. 4 hours 30 min to fully charge from dead) or 300-750 watts with Yeti Vehicle Integration Kit (appx. 1.5-4 hours), and up to 50amp/600watt solar charge input
  • Size: 15.25” Wide x 9.86” Tall x 10.23” Deep
  • Power Output: 1500 watt continuous (3000 watt surge) Inverter capable of putting out up to 12.5 Amps at 110VAC. Can output 15 Amps at 12VDC.
  • Output Ports: 2. 12.5 amp 110VAC outlets, 1- 15 amp 12VDC car ports (plus 1- 15 amp DC power pole 1. 10 amp DC 6mm jack), 2. USB-C 2. USB-A outputs
  • Expandable. there are hook-ups to tie-in additional lead-acid/AGM/Gel batteries to double (or triple, etc.) the capacity if needed, provided the additional batteries are of a similar 90 amp hour size
  • Battery is user replaceable and expandable

Goal Zero Yeti 1500X

  • Usable Capacity: 1516 watt hours or 140.4 amp hours (10.8V) = appx 1213 usable watts or 112.32 usable amp hours (at recommended 80% max discharge)
  • DC Charge Rate: 120 watts at 12V with standard factory car charger (appx. 14 hours to fully charge from dead) or 300-750 watts with Yeti Vehicle Integration Kit (appx. 2-5 hours), and up to 50amp/600watt solar charge input
  • Size: 15.25” Wide x 10.37” Tall x 10.23” Deep
  • Power Output: 2000 watt continuous (3500 watt surge) Inverter putting out 16.5 amp at 120VAC. Can output 13 Amp at 12VDC
  • Feature Set:
  • Output Ports: 2. USB-A, 2. USB-C, 2. 120VAC, 1. 13 amp 12VDC car port, 1. 10 amp 12v 6mm port, 1. 10 amp 12v power pole port
  • Battery is user replaceable and expandable

For a more detailed walkthrough of using solar generators for camping be sure to check out our guide: Everything You Need to Know About Solar Generators for Camping.

Why was A solar generator the perfect off grid dual battery setup for our truck camping build?

  • It could run a microwave, blender, a number of power tools, and charge laptops etc.

We took the time to hard-wire a dedicated 15 amp 12v DC charging port for our solar generator directly from our truck’s starting battery using the factory car charging cable, a 20 amp in-line fuse, 10 gauge pos./neg. wires, and a relay switch that only “opened” the DC charge to the unit while the truck was running.

The diagram below shows roughly how this was done.

But you can simply plug your solar generator’s car charging cable into your 12v outlet on your vehicle and have an instant dual battery setup!

We also used a 100 watt solar panel to keep things topped off when stationary. This usually offset the power consumption of our fridge while off grid for extended periods, allowing us to stay out longer without the need to idle the truck to recharge the solar generator.

Having a reliable dual battery system while camping off grid is incredibly valuable and can really improve your comfort level while truck bed camping and traveling, and we hope this guide has helped you select the best dual battery setup for your adventures.

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And as always, thanks for reading!


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