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The ultimate guide to dual-battery systems

How do you power your campsite without running your vehicle's primary battery flat? Wth a dual battery system, that's how.

If you’re heading off-road for a 4x4 camping trip then you need auxiliary power. A dual battery system – two separate batteries working in conjunction with each other but for different purposes – will ensure your vehicle has start-up power and that your campsite has consistent power.

It’s necessary to have a second battery, so you’ll always be able to start up your vehicle with your original battery and, using your second battery, you’ll also be able to optimise available power at camp and minimise any risk of running out of power while using your fridge, lights and any other camp accessories.

To understand what a dual battery setup is and to find out which is the best system for your campervan, Landcruiser, Prado, Amarok or just about anything, then read on.


What is a dual battery and how does it work?

A dual battery simply describes a battery system with a second or auxiliary battery that has been installed in addition to the vehicle’s original factory-fitted battery. 

The auxiliary battery should be positioned on a purpose-built tray, as pictured, or a battery box. (Image credit: ARB). The auxiliary battery should be positioned on a purpose-built tray, as pictured, or a battery box. (Image credit: ARB).

The second battery is usually placed in a dedicated space on a purpose-built tray in a vehicle’s engine bay, or in the cabin, or in the tray (if it’s a ute), or load space at the rear.

The aim of the extra power supply is to provide your campsite with readily available consistent power, while not draining your main battery. Usually, a dual battery setup for a fridge is an off-road tourer’s ‘first cab off the rank’ in the realm of auxiliary power because keeping your food (and beers!) cold in a portable fridge are a crucial ingredient in any happy trip away.

A dual battery can be located in an engine bay, in a vehicle cabin or in a load space, as pictured in this Amarok. (Image credit: Jarryd Sullivan). A dual battery can be located in an engine bay, in a vehicle cabin or in a load space, as pictured in this Amarok. (Image credit: Jarryd Sullivan).

A dual battery setup involves more than just installing a second battery though. The two batteries – your vehicle’s starting battery and your auxiliary battery – are two separate, isolated systems. Your vehicle’s battery and alternator* are responsible for powering all vehicle-based gear while the engine is running; your second battery is responsible for powering all other camp-based gear, such as your 12V portable fridge, lights, laptops, inverters etc, when you are stopped and turned the ignition off. (*The alternator charges both batteries.)

For correct operation, a dual battery setup needs a battery isolator. (Image credit: Ironman 4x4). For correct operation, a dual battery setup needs a battery isolator. (Image credit: Ironman 4x4).

A real-world dual battery setup will include a dual battery isolator, a dual battery monitor, all the necessary wiring and more. A dual battery isolator ensures that the two batteries are charged in order to keep the two power supplies topped up and working.

A dual battery monitor, which allows the user to check voltage levels on both batteries just by checking an in-cabin read-out, is also key to maintaining convenient awareness and electronic control over the dual battery system at all times.

There are plenty of dual battery setups available – including the Redarc dual battery system

– and reputable Aussie companies, such as Ironman 4x4, ARB, Redarc and Projecta, are known for making top-quality electrical systems and battery-related products.

Please note: An OME twin start-up battery setup – in which both batteries are intended as start-up batteries only – is not a dual-battery system, but the wiring can be sorted out to suit that system.

 

How do you install a dual battery? 

A dual battery tray should be well-designed and -built like this one from Ironman 4x4. (Image credit: Ironman 4x4). A dual battery tray should be well-designed and -built like this one from Ironman 4x4. (Image credit: Ironman 4x4).

This is really a job for the professionals but if you’re decent with the tools and know your way around a vehicle – and can get your head around a dual battery wiring diagram – then by all means give a dual battery installation a whirl.

First, you need space enough for a dual battery setup – either in your engine bay, in the cabin of your vehicle or in the tray (if you have a ute).

A large deep-cycle battery needs a strong support and that usually comes in the form of a 3mm powder-coated steel tray* on which the second battery will sit atop. That steel tray should be built to cop and absorb hard-core off-road punishment in order to protect the battery. If you’ve ever peeked under the bonnet of an outback touring Hilux and had a gander at its dual battery tray, or check out a Ford Ranger dual battery, you’ll have the right idea. (*If your dual battery is positioned in a tub or load space, it can be fitted into a laser-cut, folded and welded dual battery box.)

One of ARB's top-quality battery boxes. (Image credit: ARB). One of ARB's top-quality battery boxes. (Image credit: ARB).

Make sure you position your second battery right away from any heat sources, e.g. engine components that will become red-hot during trips etc.

As for wiring and switchgear, in simple terms, a manual four-way switching approach relies on the user to dictate the operational status of the battery: either its duty is to start the vehicle or to maintain power to the campsite. This system’s switch can be moved to a position where both batteries are being charged.

Automatic solenoid switching – by way of a solenoid attached to your off-roader’s ignition wiring – will ensure the auxiliary battery is disconnected from the main battery when you turn off the vehicle’s engine and, when engine is switched back on, it is reconnected to the engine and recharged.

Check Aussie companies, such as Ironman 4x4, ARB, Redarc, Piranha and the like, for the best electrical system support set-ups around. You can buy the gear from them or have them install it for you.

What dual battery options are available?

For off-road touring, camping and caravanning, deep-cycle batteries are your best bet. There are several types of deep cycle batteries but AGM (Absorbed Glass Mat) examples are considered the best and most versatile for fitment and use in off-roaders. 

Many off-road tourers now opt for a combination of dual battery- and solar panel-generated power. (Image credit: Southern Cross Camper Trailers). Many off-road tourers now opt for a combination of dual battery- and solar panel-generated power. (Image credit: Southern Cross Camper Trailers).

Your choice of the best options for different scenarios/vehicle types hinges on how much power you will need to draw on at your campsite. Tourers nowadays often opt for a combination of auxiliary battery power and the use of solar panels or mats, rather than only relying on onboard batteries. Solar panels or flexible mats provide a great source of auxiliary power, but alone are no substitute for a comprehensive top-quality dual battery kit – all of these bits of equipment should be considered as parts of the power puzzle and used in conjunction with each other.

Also, check out a portable power pack as a handy power source, an adjunct to your main power supplies.

A deep-cycle battery alone can cost from $216 (for a 32AH 12V AGM deep cycle battery); and a dual-battery system is likely to set you back at least $900 (fitted) or more.


Problems

Be aware that the second battery, its tray – no matter how robust it is – and the battery’s wiring and related electrical system may suffer damage due to engine bay heat, extreme temperatures, the violent repeated vibrations of outback corrugations, water, dirt or mud ingress and more.

Heading off-road can be tough on a vehicle, so make sure you buy the best dual battery setup you can find to power your campsite. (Image credit: Signature Campers). Heading off-road can be tough on a vehicle, so make sure you buy the best dual battery setup you can find to power your campsite. (Image credit: Signature Campers).

The rough nature of off-roading dictates that you should spend as much as your budget allows on the best quality gear you can find in order to enjoy your bush and beach adventures without fear of power failure.


Where can you buy a dual battery?

Ironman 4x4

ARB

Redarc

Piranha

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