What battery charger do you need for your dual battery system? You might just need to install a dual battery isolator, or you might need a DCDC charger for your 12v setup - especially if you're running a portable solar panel!

A reliable 12v system will help you power your fridge at camp, charge your devices and keep you in the bush longer

12vShauno's got more than a few 12v systems under his belt, so he's run through some of them to help you find the right dual battery charger for your 12v setup!

If we knew this trick years ago, it would have saved us thousands of dollars having to buy new batteries. So many people are using the wrong type of battery charger for their type of battery and camp setup, which results in killing their batteries prematurely without them even knowing.

We show you all the different battery chargers Shauno runs in each of his 4WDs and how they will help make your dual batteries last as long as possible and ensure that you have always got power at your campsite!


Deep cycle batteries have a maximum amount of current and voltage that they can be charged at, and many people think the faster you charge a battery is better but is not the case for every battery on the market.

Each battery type and brand have a very specific set of voltage parameters that it needs to be charged at. Most lead acid deep cycle batteries – like standard AGM or wet cell batteries – can only handle a maximum of 14.6v and 30amps of charge. Any more than this can quite literally cook your battery. Lithium batteries also have different specifications, and you can find your charging specifications of your battery when you purchase it or by doing a google search of your battery model number.


Starting with the simplest and most basic form of dual battery charging – like in Shauno’s 47 Series Farm Truck – is the dual battery isolator. When you turn on your 4WD, the charge from your alternator will charge your starter battery and your second battery. The moment you turn off your vehicle, it will isolate your second battery so it does not drain your starter battery, meaning you can always turn on your vehicle no matter how low your second battery gets.

There is a stack of benefits when it comes to a basic isolator with it being the cheapest as well as the easiest to install. However, they are limited by how much charge your alternator produces and they only suit older vehicles with fix voltage alternators.

As the name suggests, fixed voltage alternators have a constant voltage that doesn’t fluctuate. Dual battery isolators turn on and off based on the voltage it receives. Battery isolators only work with fixed charge alternators.

battery isolator

Smart Alternators

Modern 4WDs have what is called a smart alternator that trickle charge your main battery based on how much voltage is in that battery, and as they trickle charge, the smart alternator turns on and off to put less strain on your engine and fuel consumption. Battery isolators do not work properly or effectively with smart alternators, so you will need another form of battery charger if your 4WD has one.

However, smart alternators do not work well with battery isolators because it initially recharges the starter battery at 14v, and then drops down to charge of around 13.3v because the starter battery is fully charged. Battery isolators turn on at 13.2v and turn off at 12.7v, so as your alternator changes voltage it will turn your battery charger on and off without fully charging your second battery.

who can use battery isolator

Isolator – The Verdict

Battery isolators are great for older vehicles, but certainly aren’t for everyone because they do not have voltage and current control. If you have a new vehicle, or maybe just want a longer life out of your deep cycle battery, you need to upgrade to the next level of battery charger.


The main difference between a DC-DC Charger and a Battery Isolator is that a DC-DC Chargers actually controls the voltage and current going into your auxiliary battery. As mentioned earlier, batteries have a maximum current and voltage they are able to handle, however charging is much more complicated than just putting as much power into as quick as it can handle.

Stage Charging

stage charge chart agm battery

DC-DC Chargers can charge your batteries in stages. The first stage – Boost - puts in big current to fast charge and get the battery to about 80%. The second stage – Absorption - will reduce the current and increase voltage to get the battery to 100%. The third stage – Float – will change the state of charge when at 100% where it trickle-charges a small amount of voltage and current to maintain a full battery, protecting your battery from over-charging and preserves your batteries life.

What Size Charger Do You Need?

You should get the fastest charger your battery can handle. You can run smaller chargers that are lower than your batteries max charge specifications, but it will take a lot longer to charge your battery(s), so we recommend the highest amp rated DC-DC charger your set up can handle.

 If you have a regular AGM battery that can handle 14.6v and 30amps of charge for example, you should get a charger with 25-30amps of charging power. If you run two of these batteries, your battery bank can handle 60amps of charge, meaning you can run a 50amp DC-DC charge.

DC-DC Charger – The Verdict

We recommend this style of chargers for any dual battery setups as they are far safer and more effective with charging your second battery and can be used to maximise charging speed. The only downside to DC-DC Chargers is that they often do not have a readable monitor for your 12v performance. But they give you peace of mind that your battery will always be full and healthy when you arrive at camp!


Picture yourself driving around your 4WD without a fuel gauge, you would probably risk driving to the shops and back home, but you wouldn’t risk it on a big trip – that is exactly like your 12v setup. If you do not have a battery monitor or some sort of system to tell you what your battery and charging system are doing. You can go on shorter trips fine, but you can’t go to places like Cape York or the Simpson Desert with full confidence in your 12v setup.

Shauno’s 80 Series, Sooty, is set up for any big trip around Australia, largely thanks to his battery monitoring system installed for his dual battery system. His monitor allows him to charge like a regular 30amp DC-DC charger, while being able to keep an eye on his battery percentage and charge rate, as well as other things.

Often battery management systems come with an in-built 240v charger to plug into the wall of your shed at home to keep the battery topped up in between trips if need be. Shauno often has some of his 4WDs sitting without being driven for a few months between trips, and once forgot to plug in Sooty’s 240v charger which killed his 2 extra AGM batteries – a very expensive mistake.

Battery management systems are perfect for Caravans and Camper trailers, or even your 4WD that isn’t a daily driven vehicle because the battery doesn’t get recharged daily from the alternator, you can charge from a house socket, and you can monitor the state of your battery at all times.

What Gets Monitored?

Battery monitors show you 3 main things about your 12v system: how much charge your battery has left (percentage and hours left of charge), how many amps your accessories are drawing, and how much charge is going into your system from either solar or your alternator.

Basic Voltage Monitors

If you have a regular voltage monitor that only displays your batteries current voltage, here is a charge chart for a typical AGM deep cycle battery for its voltages correlating percentage:

agm battery % and V

Once your AGM battery reads 12v, your battery is about 50% discharged and it will need charging as soon as possible to avoid damaging the battery. If your battery is at 10v, that is equivalent to 0% and will be flat. Although you can recharge the battery up again, it will never be as good as new because AGM batteries ideally should never be discharged below 50%.


Solar controller come in different styles; either Pulse Width Modulation (PWM) or Maximum Power Point Tracking (MPPT). Both controllers can be effective in charging and maintaining your batteries, but MPPT is considered to be a more efficient option.

Solar can be a great addition to your 12v setup, either in addition to your battery isolator, piggybacking off your solar compatible DC-DC Charger, or on its own. Remember to keep in mind you only get good quality charge in full sun with no shade on the panels – so they are very handy when parked up at camp.

Solar panels can be mounted full time to the roof of your vehicle, keeping your battery topped up at camp (just don’t park in the shade) or when your 4WD is parked in the driveway. You can also opt to use folding solar panels or solar blankets with a long connection to your controller to put in the sunniest spot at camp to keep your battery full and happy.


Lithium batteries are known to not be the cheapest batteries on the market but offer a cost-effective battery style in the long run. Just remember when choosing a Lithium battery or if you own one already, make sure your DC-DC charger and/or Solar controller are Lithium compatible. Have a read of the rundown and comparison testing we did for AGM vs Lithium Batteries if you want more information!


With all the information here you should be able to decide what 12v set up is the best for your implication. Whether you are on a budget with an older 4WD, the battery isolator could be perfect for you, or if you use your 4WD on big remote trips, a DC-DC charger will give you confidence your battery will be perfectly healthy at every campsite. Pair either of these with solar as well to give charge when you are parked up for a few days and give you even more faith in your 12v system!