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Dual battery system information

What is a Dual Battery System?

A dual battery system is a vehicle battery system that uses a secondary battery in addition to the vehicle’s main starter battery.

The main starter battery is responsible for starting the engine and powering the vehicle’s essential electrical systems when the engine is running.

The secondary battery (often referred to as the Dual Battery) is used to power non-essential electrical systems when the engine is off, such as a fridge, lights, or a camping gear. Many tradies use their dual battery system to charge their power tools whilst on the worksite and it’s a great way to keep the kids devices charged too.

A dual battery system allows you to run auxiliary equipment without draining the main starter battery. This is important because if the main starter battery dies, you won’t be able to start your vehicle.

What battery options are there?

Lithium batteries are increasingly popular for dual battery systems, particularly where their slimline design suits installation behind the rear seats in a dual-cab ute. Whilst slimline lithium batteries are generally not suitable for starting the engine if the main starter battery goes flat, or operating a vehicle recovery winch, they’re able to run a fridge, camp lights or even an induction stove top, oven or coffee machine.

Traditional AGM deep cycle batteries are also used in dual battery systems, although their size means they’re often unsuitable for mounting behind the rear seats.

How is the secondary battery charged?

The second battery needs to be kept charged to prevent it going flat and this is normally done by either the vehicle’s alternator, an in-vehicle battery charger, a solar panel, or a combination of these.

The most common method of charging a lithium secondary battery is to use an in-vehicle battery charger which, draws power from the vehicle’s main battery system and delivers charging current (electrical power) to the secondary battery in a controlled manner. Many in-vehicle battery chargers such as the Redarc BCDC range, the Intervolt BCDC Pro and the Enerdrive range of chargers feature a special lithium battery charging mode to help preserve your investment for as long as possible.

Many AusMotion dual battery mounting brackets and dual battery trays include pre-cut holes to fit a Redarc or Intervolt battery charger alongside the battery. Where this isn’t possible, we offer a range of charger brackets to secure it under the rear seat or on the back wall of the cab.

Where is the dual battery fitted?

For vehicles without an aftermarket canopy, the most common locations to install a dual battery in a modern 4WD are behind the rear seats or in the tub. Whilst some vehicles have some space under the bonnet where a secondary battery can be fitted, they are often limited in size and risk exposing the battery and charger electronics to the intense heat of the engine, particularly in Australia’s tough climate.

Behind Seat Dual Battery Systems

By positioning the dual battery system behind the rear seats, the battery and charger benefit from a cool and air-conditioned environment while the car is in operation and the battery is being charged. While modern lithium battery systems manufactured by leading Australian companies are designed to withstand various challenging charging conditions reliably, some vehicle owners choose to install their lithium battery elsewhere, such as in a battery box located at the rear of the vehicle.

Among the most popular AusMotion dual battery products are behind seat lithium battery trays, available for most current model dual cab utes to fit a range of batteries from Australia’s favourite brands. There are AusMotion dual battery trays that provide a secure mounting for Amptron, Baintech, Custom Lithium, DCS, Dingo Box, iTech World, VoltX and many more popular lithium batteries.

In certain cases, some dual-cab utes like the 2023 VW Amarok lack sufficient space behind the rear seats to accommodate even the slimmest secondary battery. As a result, owners of such vehicles often choose to install the secondary battery in a dual battery box located at the rear of the vehicle.

In-Tub Dual Battery Box

Many vehicle owners decide to install their dual battery in a battery box mounted in the rear of the vehicle. This is a great option for those who want to use an AGM battery or a lithium battery in a more traditional battery case – Something that you’ll need to do if you want to use a battery such as the Safiery, Enerdrive or Hardkorr lithium batteries which, are not currently available in a super-slim battery case to fit behind the rear seat.
One advantage of a battery box is that many include auxiliary connections such as Anderson plugs, USB outlets and 12V connections to power your 4WD accessories and camping gear. This can save time during installation and means you don’t have to worry about mounting these power outlets somewhere else in the vehicle.

Another benefit of a dual battery box is that you can easily lift it out of the car to power 12V lights or 12V fridge whilst camping. Combined with a free-standing solar panel or solar blanket, it can sit at camp charging during the day then provide your camp with power at night.

If starting out on your 4WD adventures for the first time, a cheaper AGM battery in a battery box is a good starting point as it often allows you to upgrade to a higher capacity lithium battery later, without needing to change the wiring, battery charger, mounting location or battery box – If you’re thinking of installing an AGM battery and upgrading later, consider this when designing your wiring and selecting the charger as these can often be re-used after you upgrade to a lithium dual battery system.

There’s a large range of AusMotion dual battery box mounts available for Toyota Hilux, VW Amarok and Ford Ranger which can be installed easily by someone with only basic mechanical tools and skills.

In-Tub Dual Battery Trays

What’s the biggest lithium battery that can be fitted? is a question many 4WD owners ask. But perhaps the question should be “what size lithium battery do I need?” because it’s often easy to assume you need more battery capacity than you really do.

For most people running a fridge for a weekend camping trip, or a tradie wanting to keep drinks cold on-site each day, 100Ah or less will be sufficient.

For those wanting to use an induction hob, run a large fridge for several days or even an ice-maker or coffee machine more power will be needed (and probably an inverter too).

The iTechWorld 240X Pro is an example of a large capacity lithium battery that fits well in the space toward the rear of a Next-gen Ranger or Ranger Raptor.