Western Australia offers some of the world's most spectacular 4WD adventures—from the pristine beaches of Lancelin and Coral Bay to the rugged tracks of the Gibb River Road and Cape to Cape. But all that adventure requires power: fridges to keep food cold, lights for camp, phones for emergencies, and winches for recovery. That's where a dual battery system becomes essential.
As Perth's 24/7 battery specialists, we've installed hundreds of dual battery systems for local 4WD enthusiasts. This comprehensive guide covers everything you need to know about selecting, sizing, and installing the right system for your adventures.
Quick Answer: Do You Need a Dual Battery System?
Yes, if you: Run a camping fridge, use accessories with the engine off, go remote camping, or have a winch. A dual battery system protects your starter battery and ensures you're never stranded.
Expert consultation available: 0451 664 698
In This Guide
What is a Dual Battery System?
A dual battery system adds a second battery (called an auxiliary or house battery) to your 4WD, separate from your main starter battery. This auxiliary battery powers accessories like fridges, lights, and USB chargers while protecting your starter battery from being drained.
The system includes three key components:
- Auxiliary Battery: A deep-cycle battery designed for slow, sustained discharge
- Charging System: Either an isolator or DC-DC charger that manages power flow
- Wiring & Mounting: Heavy-gauge cables, fuses, and a secure battery tray
How It Works
When your engine runs, both batteries charge from the alternator. When you stop, the charging system isolates the starter battery, protecting it while your accessories drain only the auxiliary battery. This means you'll always have enough power to start your engine—even after running the fridge all night.
Why Perth 4WD Owners Need Dual Batteries
Perth is uniquely positioned as the gateway to Western Australia's incredible 4WD destinations. But these remote locations present specific challenges that make dual battery systems essential:
Popular WA 4WD Destinations Requiring Dual Batteries
- Lancelin Sand Dunes
- Coral Bay & Ningaloo
- Gibb River Road
- Cape Range National Park
- Francois Peron NP
- Cape Leveque
- Holland Track
- Mundaring Powerlines
- Esperance Beach Tracks
- Cape to Cape
- Steep Point
- Karijini National Park
Key Reasons You Need a Dual Battery System
- Fridge Power: A 40L camping fridge draws 1-3 amps continuously—draining a single battery overnight
- Remote Recovery: If you're stuck in sand at Lancelin, you need a fully-charged starter battery for your winch
- No Roadside Assistance: Good luck getting a jump start on the Gibb River Road
- Perth Heat: Our extreme summer temperatures already stress batteries—adding accessories compounds the problem
- Device Charging: Phones, cameras, drones, and GPS units all need power
- LED Lighting: Camp lights, light bars, and work lights require reliable auxiliary power
- Peace of Mind: Never worry about a flat battery stranding you in the middle of nowhere
The Cost of Being Stranded
We've received calls from 4WD owners stranded on remote WA beaches because they ran their fridge off their starter battery. Recovery costs from remote locations can exceed $2,000—far more than a proper dual battery system. Don't learn this lesson the hard way.
Dual Battery System Types Explained
There are three main ways to connect an auxiliary battery to your 4WD. Each has distinct advantages depending on your vehicle, budget, and requirements.
1. Voltage-Sensing Relay (VSR) / Solenoid Isolator
VSR / Solenoid Isolator
The simplest and most affordable option. A voltage-sensing relay automatically connects both batteries when the engine runs (detecting voltage rise) and isolates them when the engine stops.
- Best for: Older 4WDs (pre-2015) with conventional alternators
- Cost: $150-$400 (parts only)
- Brands: Redarc SBI, Projecta VSR, Narva
- Limitations: Not compatible with smart alternators or lithium batteries
2. DC-DC Charger (Recommended)
DC-DC Charger
The modern gold standard for dual battery systems. A DC-DC charger actively manages the charging process, converting voltage and current to optimally charge your auxiliary battery regardless of alternator type.
- Best for: Modern 4WDs with smart alternators, lithium batteries, or solar panels
- Cost: $350-$800 (unit only)
- Brands: REDARC BCDC, Enerdrive, Victron, Projecta IDC
- Advantages: Works with all battery types, smart alternator compatible, solar input available
3. Battery Management System (BMS)
Full Battery Management System
A comprehensive solution that integrates DC-DC charging, solar regulation, AC charging, battery monitoring, and load management in one unit. Ideal for touring setups and caravans.
- Best for: Serious tourers, caravan setups, multiple battery banks
- Cost: $800-$2,000+ (unit only)
- Brands: REDARC Manager30, Enerdrive ePOWER, Victron MultiPlus
- Advantages: All-in-one solution, advanced monitoring, multiple charging sources
Comparison: Isolator vs DC-DC Charger
| Feature | VSR Isolator | DC-DC Charger | Winner |
|---|---|---|---|
| Upfront Cost | $150-$400 | $350-$800 | Isolator |
| Smart Alternator Compatibility | No - may not charge properly | Yes - designed for it | DC-DC |
| Lithium Battery Support | No - can damage lithium | Yes - specific profiles | DC-DC |
| Charging Efficiency | 60-70% | 90-98% | DC-DC |
| Solar Input | Requires separate regulator | Often built-in (MPPT) | DC-DC |
| Installation Complexity | Simple | Moderate | Isolator |
| Battery Full Charge | Rarely achieves 100% | Multi-stage charging to 100% | DC-DC |
| Battery Lifespan Impact | May shorten lifespan | Optimises battery health | DC-DC |
Our Recommendation
For most Perth 4WD owners, we recommend a DC-DC charger. Modern 4WDs (Toyota HiLux, Ford Ranger, Mitsubishi Triton, Isuzu D-MAX from 2015+) use smart alternators that don't work properly with simple isolators. The extra cost of a DC-DC charger is quickly recovered through better battery health and longer lifespan.
Source: Battery Council International - Deep Cycle Battery Guide
Choosing the Right Auxiliary Battery
The auxiliary battery is the heart of your dual battery system. Unlike your starter battery (designed for short, high-current bursts), an auxiliary battery must handle deep discharges over extended periods. Choosing the right type is crucial for performance and longevity.
Auxiliary Battery Types Compared
| Battery Type | Cost (100Ah) | Weight | Lifespan | Depth of Discharge | Best For |
|---|---|---|---|---|---|
| Flooded Lead-Acid | $200-$350 | 30kg | 2-3 years | 50% | Budget setups, occasional use |
| AGM Deep Cycle | $350-$600 | 28kg | 4-6 years | 50-80% | Most 4WD applications |
| Gel Deep Cycle | $400-$700 | 32kg | 5-7 years | 50-80% | Extreme heat, minimal ventilation |
| Lithium (LiFePO4) | $900-$2,000 | 12kg | 8-15 years | 80-100% | Weight-conscious, heavy users |
AGM vs Lithium: The Modern Choice
For most Perth 4WD owners, the decision comes down to AGM or Lithium (LiFePO4). Here's a detailed comparison:
AGM Deep Cycle
- Lower upfront cost ($350-$600)
- Works with any charging system
- Proven, reliable technology
- Performs well in Perth heat
- No special charger required
- Easy to replace
- Good for occasional 4WD use
Best choice for: Weekend warriors, budget-conscious buyers
Lithium (LiFePO4)
- 60% lighter than AGM
- 2-3x longer lifespan
- 100% usable capacity
- Faster charging
- More cycles (2000+)
- Flat discharge curve
- Better long-term value
Best choice for: Frequent tourers, weight-sensitive setups
Important: Lithium Requires DC-DC
Lithium batteries cannot be used with simple isolators. They require a DC-DC charger with a lithium-specific charging profile. Using an isolator with lithium will damage the battery and void the warranty. We cover this in more detail in our AGM vs Lead-Acid guide.
Our Recommended Batteries for Perth 4WDs
Budget Option
$280-$400 installedCentury Deep Cycle N70T
- 105Ah capacity
- Flooded deep cycle
- 12-month warranty
- Good for occasional camping
Best Value
$450-$650 installedSupercharge AGM Deep Cycle
- 120Ah capacity
- AGM sealed construction
- 24-month warranty
- Ideal for regular 4WD use
Premium Choice
$1,200-$1,800 installedEnerdrive ePOWER Lithium
- 100Ah usable capacity
- Built-in BMS
- 5-year warranty
- Serious touring setups
How to Size Your Dual Battery System
Undersizing your system means running out of power; oversizing wastes money. Here's how to calculate exactly what you need.
Step 1: Calculate Your Power Consumption
List all devices you'll run from your auxiliary battery and their power draw:
Example: Typical Perth Camping Setup
| Device | Power Draw | Hours/Day | Ah/Day |
| 40L Fridge (Engel/Waeco) | 2.5A average | 24 | 60Ah |
| LED Camp Lights | 1A | 4 | 4Ah |
| Phone/Device Charging | 2A | 2 | 4Ah |
| Water Pump | 4A | 0.5 | 2Ah |
| Total Daily Consumption | 70Ah | ||
Step 2: Apply the 50% Rule (For AGM)
AGM batteries should only be discharged to 50% for maximum lifespan. This means you need double your daily consumption in battery capacity.
Calculation: 70Ah daily × 2 (50% rule) = 140Ah battery minimum
Lithium Advantage
With lithium batteries, you can use 80-100% of capacity. The same 70Ah daily load only requires an 80-100Ah lithium battery—half the size and weight of an equivalent AGM setup.
Step 3: Consider Recharge Time
Your DC-DC charger needs to replenish the battery during driving. A typical DC-DC charger outputs 25-40A:
- 25A charger: Recharges 70Ah in approximately 3 hours of driving
- 40A charger: Recharges 70Ah in approximately 2 hours of driving
If you're doing short drives between camps, consider a larger charger or adding solar.
Recommended System Sizes
| Use Case | Daily Load | AGM Size | Lithium Size | DC-DC Charger |
|---|---|---|---|---|
| Light (Fridge + Lights) | 40-50Ah | 100Ah | 60Ah | 25A |
| Medium (+ Devices, Pump) | 60-80Ah | 135-150Ah | 100Ah | 40A |
| Heavy (+ Inverter, Tools) | 100-150Ah | 200Ah+ | 150Ah | 50A+ |
| Extreme (Full Touring) | 150Ah+ | 300Ah+ | 200Ah+ | 60A+ / Solar |
Popular Setups for WA Adventures
Based on hundreds of installations for Perth 4WD owners, here are our most popular dual battery configurations:
Weekend Warrior
$800-$1,200 installedPerfect for: Lancelin trips, overnight camping, occasional beach runs
- 100-120Ah AGM battery
- REDARC BCDC1225D (25A DC-DC)
- Under-bonnet or tray mount
- Anderson plug outlets
Supports: Fridge, lights, phone charging
Outback Tourer
$1,500-$2,200 installedPerfect for: Gibb River Road, Coral Bay, week-long trips
- 135-150Ah AGM battery
- REDARC BCDC1240D (40A DC-DC)
- 160W solar panel + MPPT
- Battery monitor (Victron/REDARC)
Supports: Fridge, lights, devices, water pump, 12V accessories
Expedition Grade
$3,500-$5,000+ installedPerfect for: Extended touring, remote work, off-grid living
- 200Ah+ Lithium (LiFePO4)
- REDARC Manager30 or Enerdrive system
- 300W+ solar array
- 2000W inverter
- Comprehensive monitoring
Supports: Everything + laptops, power tools, coffee machines
Vehicle-Specific Considerations
Different 4WDs have different dual battery mounting options and requirements:
| Vehicle | Common Mount Location | Smart Alternator? | Notes |
|---|---|---|---|
| Toyota HiLux (N80) | Under-bonnet tray | Yes (2015+) | Excellent factory dual battery options via ARB |
| Ford Ranger (PX3) | Under-bonnet or tray | Yes | DC-DC essential, tight engine bay |
| Toyota LandCruiser 200 | Under-bonnet tray | Yes (2016+) | Spacious engine bay, factory-ready |
| Toyota Prado 150 | Tray or cargo area | Yes (2015+) | Limited under-bonnet space |
| Mitsubishi Triton | Tray mount | Yes (2019+) | Engine bay too cramped for under-bonnet |
| Isuzu D-MAX | Under-bonnet or tray | Yes | Good ARB support available |
| Nissan Patrol Y62 | Under-bonnet tray | Yes | Excellent engine bay space |
| Toyota 70 Series | Under-bonnet | No (non-DPF models) | Isolator possible, simple installation |
Vehicle alternator data sourced from: ARB 4x4 Accessories - Dual Battery Kits
Installation Options & Costs
Dual battery installation ranges from simple DIY projects to complex professional jobs. Here's what to expect:
Professional Installation (Recommended)
- Correct cable sizing for your specific setup (undersized cables cause fires)
- Proper fusing at both battery terminals
- Secure battery mounting that meets ADR standards
- Clean, professional wiring with proper grommets and protection
- System testing to verify charging performance
- Warranty coverage on labour and installation
- Integration with your vehicle's existing systems
Installation Cost Breakdown
| System Type | Parts Cost | Labour (3-6 hrs) | Total Installed |
|---|---|---|---|
| Basic Isolator + AGM | $450-$650 | $200-$350 | $650-$1,000 |
| DC-DC Charger + AGM | $700-$1,100 | $300-$450 | $1,000-$1,550 |
| DC-DC + AGM + Solar | $1,200-$1,800 | $400-$600 | $1,600-$2,400 |
| DC-DC + Lithium | $1,600-$2,500 | $350-$500 | $1,950-$3,000 |
| Full BMS + Lithium + Solar | $2,500-$4,500 | $500-$800 | $3,000-$5,300 |
Need a Dual Battery System Installed?
We supply and install dual battery systems across Perth. Get a quote for your specific 4WD and requirements.
CALL: 0451 664 698 ONLINE QUOTEMobile service available | All Perth metro areas
DIY Installation: What You Need to Know
If you're handy with auto electrics, a basic isolator system can be DIY-installed. However, consider these factors:
DIY Considerations
- Cable sizing: Undersized cables overheat and cause fires. For a 40A system over 3m, you need minimum 6mm² (8 AWG) cable
- Fusing: Both batteries must be fused at the terminal. Missing fuses void insurance
- Warranty: Incorrect installation voids battery and charger warranties
- Insurance: Improper electrical work may void your vehicle insurance
- ADR Compliance: Auxiliary batteries must be securely mounted per Australian Design Rules
Our advice: Unless you have automotive electrical experience, professional installation is worth the investment.
Safety guidelines from: Australian Government - Vehicle Safety Standards
Maintenance Tips for Perth Climate
Perth's extreme heat is tough on batteries. We've covered this extensively in our battery life in Perth's hot climate guide, but here are dual battery-specific tips:
Monthly Checks
- Check terminal connections: Vibration loosens terminals over time
- Inspect for corrosion: Perth's coastal salt air accelerates terminal corrosion
- Verify battery voltage: Resting voltage should be 12.6V+ (AGM) or 13.2V+ (Lithium)
- Check mounting hardware: Ensure battery is securely fastened
- Clean battery top: Dust and grime can cause current leakage
Before Long Trips
- Load test: Verify both batteries hold capacity under load
- Check DC-DC operation: Confirm charging voltage reaches 14.4V+ (AGM)
- Test all outlets: Verify Anderson plugs and 12V sockets work
- Inspect wiring: Look for chafing, heat damage, or loose connections
- Top up charge: Start your trip with both batteries at 100%
Perth Summer Precautions
Heat Protection Essentials
Perth regularly exceeds 40°C in summer. Extreme heat is the #1 killer of automotive batteries. For under-bonnet mounted auxiliary batteries:
- Use a heat shield: Insulate the battery from engine heat
- Ensure airflow: Don't block ventilation around the battery
- Consider tray mounting: Batteries in ute trays run 15-20°C cooler than under-bonnet
- Use AGM or Lithium: Both handle heat better than flooded batteries
- Monitor regularly: A battery monitor alerts you to problems early
For more detail on protecting batteries in Perth heat, see our FIFO summer battery care guide.
Charging During Storage
If your 4WD sits unused for extended periods (common for FIFO workers), batteries self-discharge and sulphate:
- AGM batteries: Lose ~3% charge per month at 25°C, faster in heat
- Lithium batteries: Lose ~1-2% per month with BMS standby drain
Solution: Connect a quality maintenance charger (like CTEK or Projecta) to keep batteries healthy during storage. Some DC-DC chargers include a "supply mode" that works with an external power source.
Frequently Asked Questions
Can I run a fridge without a dual battery system?
Short answer: Not safely. A typical 40L camping fridge draws 40-60Ah over 24 hours. Your starter battery (usually 60-70Ah) would be completely drained, leaving you stranded. Even if you only run the fridge for a few hours, repeatedly deep-discharging a starter battery dramatically shortens its life.
What size fuse do I need?
Fuse sizing depends on cable size and expected load. As a general rule:
- 6mm² cable (8 AWG): Maximum 50A fuse
- 10mm² cable (6 AWG): Maximum 80A fuse
- 16mm² cable (4 AWG): Maximum 100A fuse
Always fuse within 300mm of each battery terminal. Use the lower of: cable rating or expected maximum current + 25%.
Can I charge lithium from my alternator?
Only with a DC-DC charger. Lithium batteries require specific charging profiles with voltage limits. Direct connection to an alternator (via isolator) will damage the alternator (lithium accepts current too fast) and potentially the battery. Always use a DC-DC charger with a lithium profile.
How long will my dual battery run a fridge?
Use this formula: (Battery Ah × Depth of Discharge) ÷ Fridge Amps = Hours
- 100Ah AGM at 50% DoD, 2.5A fridge: (100 × 0.5) ÷ 2.5 = 20 hours
- 100Ah Lithium at 80% DoD, 2.5A fridge: (100 × 0.8) ÷ 2.5 = 32 hours
Do I need solar with a dual battery?
Not essential, but highly recommended for extended trips. Solar supplements charging when you're stationary or driving short distances. A 160-200W panel can produce 40-60Ah per day in Perth's sunny conditions—enough to offset most camping loads without driving.
Can I use my starter battery as a deep cycle?
No. Starter batteries are designed for short, high-current bursts (cranking). Deep cycling a starter battery (discharging below 50%) destroys it quickly—often within a few cycles. Always use a dedicated deep-cycle battery for auxiliary power. We explain the differences in our AGM vs Lead-Acid battery guide.
What's the difference between 12V and 24V systems?
Most 4WDs use 12V electrical systems. Some trucks, buses, and military vehicles use 24V. Ensure all your components (fridge, charger, accessories) match your vehicle's voltage. Mixing 12V and 24V components without proper converters causes damage.
How do I know if my alternator is "smart"?
If your 4WD was manufactured after 2015, it almost certainly has a smart alternator. These alternators reduce output when the battery is charged to improve fuel economy. Check your owner's manual or contact us—we can advise for your specific vehicle.
Ready to Set Up Your Dual Battery System?
A properly configured dual battery system transforms your 4WD from a day-tripper into a capable expedition vehicle. Whether you're doing weekend runs to Lancelin or planning a lap around Australia, the peace of mind from reliable auxiliary power is invaluable.
As Perth's 24/7 battery specialists, we supply and install dual battery systems for all popular 4WDs. We'll help you size the right system for your needs, choose quality components, and ensure professional installation.
Get Your Dual Battery System Quote
Tell us about your 4WD and camping requirements. We'll recommend the right system and provide a complete installed price.
CALL NOW: 0451 664 698