Towing a fully loaded caravan up the Hume on a 38-degree day, with the fridge working hard, a 12V compressor cycling, and the camper behind pulling its own auxiliary draw, asks more of a vehicle's electrics than most buyers expect. A dual battery system built for weekend day trips will limp along in that setting, then quietly give up on night three of a longer run. The right setup, sized for the sustained current draw of towing heavy loads, keeps the starter battery protected, the fridge cold, and the driving days stress-free. Outbax has built a reputation among Australian tourers for supplying exactly that sort of kit. This guide covers what to look for, what each component actually does, and which configurations match real towing profiles on Australian roads.
What a Dual Battery System Does When You're Towing
How a Dual Battery Setup Protects Your Starter Battery
The core function of a dual battery system is separation. The cranking battery stays dedicated to starting the engine. A second auxiliary battery runs the fridge, lights, USB outlets, inverter, and any fixed 12V accessories in the vehicle or trailer. When the engine is off, the two batteries are isolated so that an overnight fridge run cannot leave you with a flat starter in the morning. That is especially valuable when you are towing, and a jump start means unhitching two and a half tonnes of van on a slope.
VoltX 12V 100Ah Blade Lithium LiFePO4 Battery
Why Towing Changes the Way Your Auxiliary Battery Works
Towing adds a sustained electrical load on top of the baseline touring draw. Trailer brake controllers, LED work lights, reversing cameras, and internal camper electrics all pull from the auxiliary side. On long driving days, the auxiliary battery cycles harder and recharges less predictably, particularly on modern utes running variable voltage alternators.
Lithium Dual Battery System vs AGM for Heavy Tow Use
Lithium iron batteries, like the VoltX 12V 100Ah LiFePO4 Battery, handle deeper and more frequent discharge cycles than AGM, at roughly a third of the weight for the same usable capacity. For a heavy tow rig where payload matters and the fridge runs 24/7, a lithium dual battery system from Outbax is almost always the more sensible long-term buy.
Here’s what one of our customers said:
“I have 4 of these (version with battery monitor) in my caravan to provide 400ah of power. They are honestly brilliant. They do actually provide the rated power, I can hammer these and they just hold up. Running them for over a year now. I highly recommend these batteries as I have the confidence in them when off grid, they run a 3000W inverter at full tilt (Pulling +280A) no problems at all. There may be cheaper and more "premium" expensive batteries out there, just get these, you won't be disappointed.”
Power Demands of Towing Heavy Loads in Australia
Calculating Daily Amp-Hour Use for Caravans and Camper Trailers
A realistic daily amp-hour budget is the starting point. A 12V compressor fridge typically draws 40 to 60Ah per 24 hours in summer. Add 10 to 15Ah for LED lighting, 5 to 10Ah for phone and camera charging, and another 15 to 20Ah if you are running a diesel heater overnight or an inverter for a CPAP machine. That puts a typical Australian caravan or camper trailer setup in the 80 to 110Ah range of real daily use.
Running 12V Fridges, Lights, and Chargers in Summer Heat
Cabin temperatures on an outback driving day regularly push past 40 degrees. Fridges work harder, duty cycles lengthen, and your 12V fridge power budget can quietly blow out. Sizing battery capacity for caravan use around the worst case, not the best, is what keeps the beer cold and the system honest.
What Your Alternator Actually Delivers While Under Tow
Many buyers assume the alternator will keep everything topped up. It will not. Smart alternator-compatible charging gear is now essential on most dual-cab utes built in the last five years, because the charge voltage at the auxiliary battery is often too low for safe lithium charging.
VoltX 12V 200Ah Pro Lithium LiFePO4 Battery
Key Components of a Reliable Dual Battery Setup
DC-DC Charger vs Battery Isolator
A basic battery isolator simply connects the two batteries when the engine runs. On older vehicles with a steady 14.2V alternator output, this is enough. On anything modern, a DC-DC charger is the right answer. It regulates the alternator voltage to deliver the correct multi-stage charge profile a lithium bank needs. It also accepts a solar input when paired with an MPPT solar controller, so the auxiliary bank keeps charging on rest days.
Choosing the Right Battery Capacity
Most heavy tow setups land on a 200Ah lithium battery for caravans, including the VoltX 12V 200Ah Pro LiFePO4 Battery, a 100Ah lithium battery for smaller camper trailers or in-cab auxiliary use, or two 100Ah units wired in parallel for flexibility. A slimline lithium battery helps in tight under-tray installs on utes where upright space is limited.
Here’s what one of our customers said:
“I’ve had these battery connected in parallel for about a year feeding a 2.5KW inverter and they have worked faultlessly over this time. I have been off grid for 4 days running aircon for about 3 hrs a day, as well as air fryer, coffee machine and everything else that runs off the 12v side, with 650 watts of solar and by the end of the week we still had 100% on battery’s. excellent buy and excellent quality.”
Power Distribution, Monitoring, and In-Cab Controls
High-current accessories such as winches, inverters and air compressors need proper wiring. The Outbax 4 Gang 300A M8 Power Distribution Block gives you a clean, high-amp bus bar to land those circuits on, which is safer and tidier than daisy chaining off the battery terminals. For live monitoring, the VoltX 12V Control Box with LED lights and built-in voltmete sits neatly on the dash or inside the camper, showing voltage at a glance while running USB devices off the same unit.
The Best Dual Battery Systems for Heavy Tow Use
Complete Kits for Caravanners and Grey Nomads
For buyers who want one decision and one box, the Outbax 2kW Dual Battery System Kit with Inverter, DC DC MPPT Controller and Lithium Battery is the straightforward pick. The 2kW pure sine wave inverter handles mains-style appliances in the van (microwave, induction cooktop on low, coffee machine in short bursts), the built-in DC-DC and MPPT charger keeps the lithium battery charged from both the alternator and roof solar, and everything is matched at the specification level so nothing is bottlenecked by the weakest component.
VoltX 12V 300Ah Pro Lithium LiFePO4 Battery
Mid-Capacity Setups for Dual Cab Utes and Camper Trailers
If your auxiliary bank is larger and you want a faster recharge on long driving legs, the 12V 50A SRNE DC-DC MPPT Charger is the right fit. A 50A DC-DC charger will refill a 200Ah lithium bank, like the VoltX 12V 200Ah Slim LiFePO4 Battery, meaningfully inside a day's drive, which matters when you are moving between free camps and relying entirely on what the alternator and solar can put back.
Expandable Systems for Solar and Off-Grid Touring
For dual-cab utes with a moderate draw and a roof or bonnet solar panel, the 12V 30A SRNE VoltX DC-DC MPPT Charger is the sweet spot. Bluetooth monitoring lets you check charge state from the cab or campsite without opening the canopy, which is a real quality-of-life feature when you are living out of the vehicle for weeks at a time.
Installation, Charging, and Monitoring on the Road
Where to Mount Your Auxiliary Battery for Towing
The under bonnet fitment is convenient but hot. Tray or canopy mounts behind the cab suit most dual-cab utes, while caravan and camper trailer batteries sit in a dedicated battery box with fuses close to the terminals. Use Anderson plugs at the tow vehicle to trailer junction, and run appropriately-sized cable to avoid voltage drop, which is the silent killer of dual battery charging while driving.
Adding Solar to Keep Ahead Of Heavy Daily Draw
A 200W to 300W panel, paired with a decent MPPT solar controller, covers the gap between what the alternator returns and what a heavy tow day actually uses. It also lets you sit in camp for three or four days without starting the vehicle.
Monitoring State of Charge So You Never Get Caught Out
A Bluetooth shunt or in-cab control box gives you a state of charge in amp-hours remaining, not just a raw voltage reading. That is the number that actually tells you whether you have another night off-grid in the tank.
Gentrax 12V 100Ah Blade Lithium LiFePO4 Battery
Choosing the Right Dual Battery System for Your Tow Setup
Heavy tow electrical demand is higher than most buyers first estimate, and the gap between a marginal setup and a properly-specified one is usually the difference between a trip that hums along and a trip spent babysitting the battery. Size the system around your worst day, not your best. Match the DC DC charger, solar controller, and battery capacity to the same standard. Then, install it cleanly with proper distribution and monitoring. For a complete range of kits and components built for Australian conditions, Outbax's 4WD dual battery collection is the sensible place to start.
