12V power for 4WD touring: batteries, charging and solar

A 12V touring power system lets you run a fridge, lights, pumps and chargers for days without mains power. The basics are: work out how much power you use per day, choose an auxiliary battery big enough to cover it with a margin, charge it while driving (usually with a DC-DC charger) and with solar while camped, and wire it safely with correctly sized cable and fuses.

This is plain-English guidance, not an installation manual. Poor wiring is a fire risk; use a qualified auto electrician for permanent installations. This guide is part of our 4WD touring guide.

Step 1: Work out your daily power use

List every device, its current draw and how many hours a day it runs. The biggest load is usually the fridge, which cycles on and off depending on the weather and how often it is opened. Lights, water pumps, phone and camera chargers, and laptops add to it.

Manufacturers publish power use for their products. Add it up to estimate daily consumption in amp-hours (Ah), then add a safety margin for hot weather.

Step 2: Choose an auxiliary battery

Auxiliary batteries power accessories without draining the starting battery.

• Lead-acid types (AGM, flooded): cheaper and heavier; should not be discharged deeply on a regular basis.
• Lithium (LiFePO4): lighter, can be discharged more deeply and handles more cycles, but costs more and needs a compatible charger.

Usable capacity matters more than the label. Check the manufacturer's guidance on recommended depth of discharge.

Step 3: Charging while driving

Older vehicles often used simple isolators that connect the auxiliary battery when the engine is running. Many modern vehicles have smart (variable voltage) alternators that may not charge an auxiliary battery properly through a simple isolator. A DC-DC charger solves this and applies the correct charging profile for the battery type. Check with an auto electrician for your vehicle.

Step 4: Solar while camped

Solar panels and blankets top up batteries at camp.

• Fixed panels on a roof or camper are always connected but cannot be angled to the sun.
• Portable panels and blankets can be moved to follow the sun and kept in sunlight while you park in shade.
• A solar regulator (controller) is needed between panel and battery, unless built into the DC-DC charger.

Output varies with season, weather, shading and angle. Size solar to replace your daily use with a margin for cloudy days.

Step 5: Inverters

Inverters convert 12V to 240V for devices like laptops and camera chargers. They are inefficient compared with 12V charging, so use 12V chargers where possible. Large inverters draw high currents and need heavy cabling. Permanent 240V wiring must be installed by a licensed electrician.

Step 6: Wiring and safety

• Use cable rated for the current and length; undersized cable causes voltage drop and heat.
• Fuse every positive cable close to the battery.
• Secure batteries so they cannot move in a crash or on corrugations.
• Protect cables from chafing, heat and water.
• Follow battery manufacturer guidance on ventilation and mounting.

Energy regulators such as Energy Safe Victoria publish electrical safety information.

Monitoring

A battery monitor shows state of charge and power use, helping you avoid running batteries flat. It is one of the most useful upgrades for touring.

Planning for remote trips

Power is part of your safety plan: it runs fridges for food, charges communications devices and keeps lights on. Carry a backup way to start the vehicle, such as a jump starter. See remote travel tips for communications and fuel planning.

Power system checklist

Where to go next

• Back to the 4WD touring guide
• Pre-trip 4WD vehicle checks
• Gear
• 4WD touring FAQ