Dual batteries 101 – We take a look at dual batteries, how they work and why it’s a handy set up to have.
First of all, let us preface this with an apology to any British readers lurking here. But frankly, warm beer is disgusting. Have you ever had a long day on the tracks, rolled into camp, and been absolutely hanging out for a warm beer? The sheer thought of it has us dry-heaving. Now that we think about it, there are not too many drinks you’d want warm. Soft drinks. Water. A cheeky glass of Rose. All of them are better cold.
The same goes for your food too. Sure, you want it hot when you’re eating it. But we’re pretty confident you won’t be keen on room-temperature chicken going into your dinner. In an ideal world, your camper or caravan’s fridge will have the answer to all your problems. But if you’re un-hitched for the day, you’ll need a dual battery system. Here’s how to ensure you’re getting what you need.
Dual battery V second battery
Depending on what tow-tug you’re lugging around your home on wheels with, you may already have a pair of batteries under the bonnet. That doesn’t mean you have a dual battery system, it could in fact just be a second battery. Because vehicle manufacturers like overly complicated things, with certain ‘rugged’ models they’d occasionally fit a second battery from the factory. This typically engaged with the ignition to double your starters voltage from 12v to 24v. Apart from that, there were no benefits.
A dual battery system, by comparison, is a completely separate electrical system running alongside the factory system. They’re charged by the same alternator but work in complete isolation from each other. The benefit of this is any accessories running off the dual battery system won’t deplete your vehicle’s start. Your fridge can run until it’s dead, and your tow-tug will still fire right up without hassle.
How do they work?
A dual battery system, in its bare elements, is an unbelievably simple thing. Think about plonking a car battery on your kitchen bench, connecting up a battery charger to the wall, and then running a small light to the battery. That’s all a dual battery system is, just with a few different components.
If it was the 1970s again and you were wiring up a dual battery system into your Series Landie, you could effectively wire the two batteries together, with a dash-mounted switch to isolate them. Flick the switch on when you’re driving to charge the battery, flick it off when you’re parked so any accessories on the dual battery system wouldn’t flatten your main battery. Forget that switch just once though and you’re dead in the water.
A smarter version, and something commercially available for decades was a simple solenoid doing the switching for you. With this system, the second battery can be used to jump-start the first. The downside though is if you’ve ran your second battery low overnight, when the solenoid engages it can draw the main battery down below a point where it’ll start the vehicle.
The most common system though, and the one you’ll find on the shelf in any accessory store, is a DC to DC charger. These work much the same as the charger you plug into your wall at home to charge a battery, except they take their power from your vehicle’s charging system rather than a wall outlet. The benefits of these two separate systems mean it’s impossible for your fridge to drain your start battery. They’re more expensive than a switch on the dash but far better for the long-term health of your second battery, and the peace of mind your tow-tug will start when you turn the key.
What about the batteries?
Just like your camper or caravan can run different styles of batteries, so too can your tow-tug. The exact type you run, typically comes down to your budget rather than your needs. Let us explain.
Lead-acid batteries
These are still the go-to for starting just about any internal combustion engine on the planet. They’ve been ticking along doing their job since the mid-1800s and will be around for a while yet. They’re cheap as chips but come with a few downsides as a result. The first, is they’re heavy buggers. Expect a 100Ah lead-acid battery to run around the 20-25kg mark. They’ll also only give you a usable voltage for around half their capacity. So while it may still have 50Ah left in the bank, it won’t be enough to run a fridge. If you’ve heard the term deep-cycle, that’s just a lead acid that is orientated towards a slow draw of power from accessories, rather than a quick draw from a starter motor.
Absorbed Glass Matt (AGM)
An AGM battery offers a few distinct benefits over old-school lead acid. The first, is they’re able to be installed in the vehicle with you. A lead-acid battery will give off fumes that can negatively affect your health, whereas an AGM won’t. This makes them better suited to installation in wagons, in drawer systems, or under the back seat in a dual cab. They’re also better able to withstand the harsh corrugations of outback travel better than lead-acid. In theory, they should be slightly lighter than a lead acid, although comparing specs to specs they’re often slightly heavy. You will pay more for an AGM battery, but they’ll last longer too.
Lithium
If you’ve got deep pockets, a Lithium dual battery setup is the bees-knees of today’s technology. They’re typically half the weight of a lead-acid battery so you can fit twice as much power on board for the same weight. They’re able to be designed into weird and wonderful shapes so they can fit behind the back seat of a dual cab. And they’re able to provide usable power all the way down to near empty. That means that for 100Ah of usable power with Lithium you’ll occupy one battery spot at around 14kg total weight. Vs a lead acid setup that’ll require two battery spots and over 50kg of weight.
Are there cheaper options?
Absolutely! Between professional wiring, monitors, chargers, mounts and the batteries themselves, a dual battery system can cost some serious coin. If you’re budget conscious, a few manufacturers are starting to produce all-in-one portable systems like the Redarc GoBlock. They’re still going to run you a pretty penny but will be significantly cheaper, and able to swap from vehicle to vehicle. If you’re really budget conscious, some are even able to take a lead-acid battery but will only be usable in ventilated areas.
