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Dual Battery System: A Beginner's Guide

Dual Battery System: A Beginner's Guide

Have you ever found yourself stranded in the middle of nowhere, with a dead battery and no power to run your essential gear? Don't let that happen again! In this comprehensive guide, we'll cover everything you need to know about dual battery systems to keep you powered up on your off-roading adventures.

Table of Contents

  1. What is a Dual Battery System?
  2. How Does Dual Battery System Work?
  3. The Pros and Cons of Installing a Dual Battery System
  4. What is the Best Dual Battery System for Me?
  5. Types of Auxiliary Batteries
  6. Installation Basics
  7. How to Keep Your System Running Smoothly

What is a Dual Battery System?

A dual battery system is a vehicle battery setup that uses a secondary battery in addition to a vehicle's starter battery . This secondary battery is used as a power source for auxiliary gear and accessories, ensuring that your vehicle has enough power for all your off-road gadgets and necessities.

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.

When your vehicle is turned off, your secondary battery powers all gear and accessories attached to your vehicle, allowing you to run your portable fridge, lights, inverters, and other devices 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, ensuring that you only draw power from one battery at a time.

Keeping each battery functioning independent of each other is crucial to preventing your starter battery from being drained and making sure your vehicle starts up every time. The battery isolator also ensures that both batteries charge properly.

Some 4x4 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. However, this feature is not available in all isolators.

Your auxiliary battery will most likely be a deep cycle battery, as these batteries are designed 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 assured that 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 other devices while the ignition is off
  • No need to worry about draining your starter battery
  • Increases power available for using your winch
  • Ability 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
  • 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, there are many options available for dual battery systems, and you can find the one that best suits your needs.

We highly recommend dual battery system Redarc for their reliable and efficient performance. As an Australian born and bred company, they provide all the electronic components needed for a dual battery system setup.

Once you have the rest of your battery kit, it's time to choose a secondary battery. There are several types of auxiliary batteries available, each with their own benefits and drawbacks.

Types of Auxiliary Batteries

Lead Deep Cycle

  • Suitable under the bonnet, or in an open tray or tub
  • Inexpensive, but may have a reduced lifespan if not fully discharged and recharged with each use


  • The popular choice among any rig
  • Suitable for any location as they do not emit hazardous gases while charging
  • Better suited to partial use and recharge, rather than fully discharging and recharging in a use cycle


  • Reduced weight and increased capacity compared to other battery types
  • Most durable battery when used in a partial use cycle
  • Cannot be fitted under the bonnet of a vehicle due to heat restrictions

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.

  1. Mount the second battery on your rig, ensuring you have enough wire to make the necessary connections to your second battery.
  2. Disconnect your starter battery.
  3. Mount the Voltage Sensitive Relay (VSR). Place the VSR close to the main battery and away from any hot or moving parts.
  4. Cut cables to length.
  5. Fit lugs to the bare ends of the 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.
  6. Use the black wire attached to the VSR to earth the relay.
  7. Connect the main battery to the VSR.
  8. Earth your second battery.
  9. Attach the VSR to the mounting plate. Positive cables may now be attached to both batteries.
  10. Attach the negative leads, first to the starter battery and then to the second battery.
  11. Test your system is working with a multimeter.

If you're looking for an all-in-one solution, consider purchasing a dual battery system kit that includes everything you need for installation, along with a comprehensive guide.

How to Keep Your System Running Smoothly

Like any component in your vehicle, your 4x4 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 ensure smooth operation.

For more information on the best dual battery systems or dual battery system prices, don't hesitate to get in touch with experts in the field to see how they can help you improve your rig today.


A dual battery system is an essential investment for any 4WD enthusiast who wants to ensure their vehicle is always ready for adventure. By understanding how dual battery systems work, the benefits they provide, and how to choose the right setup for your rig, you can enjoy the freedom and reliability that comes with having a dependable power source on your off-roading trips. With careful installation and regular maintenance, your dual battery system will keep you powered up and ready for anything the Australian outback has to offer.

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