A Landcruiser dual battery setup is one of the most effective ways to ensure your vehicle has reliable power in any situation. Modern 4WD touring and off-grid trips often rely on fridges, winches, lighting and other accessories that can drain a single battery quickly. By adding a second battery, you create a dedicated power source for these devices while keeping your starting battery ready to crank the engine.
In this guide, we explain how a dual battery system works, why it’s beneficial, and what to consider when installing one in your Landcruiser.
What Is a Dual Battery System?
A dual battery setup means adding a second 12V battery to your Landcruiser’s electrical system, so you have a bank of two batteries. These batteries are wired with a dcdc in between the batteries so that they share charging from the alternator but are electrically isolated when needed. In practice, this lets one battery (the “starter” battery) focus on cranking the engine, while the other (the “auxiliary” battery) powers accessories when the engine is off.
Key components include:
- Heavy-gauge cables
- An isolation device (like a DC-DC charger or voltage sensitive relay)
- Safety fuses
The dual battery system might use a DC-DC charger (e.g. Victron DCDC or Enerdrive dcdc) to properly charge a lithium aux battery, or a simple solenoid isolator if the vehicle does not have a smart alternator.
- Starter vs Auxiliary Battery: Typically, the factory engine-starting battery remains in place as Battery 1. The new Battery 2 is usually a deep-cycle type (or dual-purpose) placed nearby.
- Isolation/Charging: An intelligent isolator or DC-DC battery charger ensures the batteries charge properly. For example, the Victron Dcdc/Enerdrive Dcdc unit is common in Australia for charging an AGM or Lithium aux battery off the 300 Series’ alternator.
- Automatic Operation: When the engine runs, the isolator connects the batteries so both receive charge. When the engine stops, the aux battery is isolated to prevent it from draining the starter battery.
This setup means you essentially have twice the available capacity and power. If one battery fails or gets drained, the other can still start the engine or supply power. In a 300 Series Cruiser, which may be loaded with lights, fridges, air compressors and more, a dual system is a reliable way to handle the electrical load without risk.
Why Fit a Dual Battery in Your 300 Series Landcruiser?
A dual battery setup offers significant advantages for a 300 Series Landcruiser, particularly for those who tour, camp, or spend extended time off-grid. With two batteries, you reduce the risk of being stranded with a flat starting battery after running accessories overnight. Even if one battery is drained – for instance, by a fridge running continuously – the other retains enough charge to crank the engine and then charge both batteries.
A dedicated auxiliary battery allows you to power 12V fridges, lights, winches, radios and other battery accessories without affecting the main starting battery. This means you can set up camp, run your gear, and still start your vehicle the next morning.
The 300 Series features a high-output 200A alternator, making it well-suited for dual-battery charging. A properly installed system also provides redundancy and greater reliability. For example, Batteries Sunshine Coast recently fitted a dual battery in a 300 Series and noted the updated battery tray requires precise component placement for a seamless fit.
In emergencies, many systems feature a jump-start link, letting the auxiliary battery start the engine if the main one is flat.
How Dual Batteries Are Wired (Setup Overview)
A typical dual battery install on a 300 Series Landcruiser will include:
- Two 12V Batteries: Often the factory battery stays in the OEM location under the bonnet. The second battery may be placed in the engine bay (as with many under-hood kits) or in the rear cargo area.
- Mounting Tray/Brackets: The new LandCruiser 300 Series has a redesigned battery tray. Use the existing battery mounting points so no drilling is required, and everything fits under the factory battery cover. Batteries Sunshine Coast installed two PowerAGM batteries in one LC300 without altering the engine bay; the space restrictions mean compact batteries are ideal.
- Cables: Heavy gauge positive and negative cables run between the two batteries and to the isolator. Negative (ground) wires should be well bolted to chassis points.
- Isolation Device: A DC-DC charger or a battery isolator switch goes between the batteries. This device allows charge current to flow to the aux battery only when the alternator is charging, and isolates it when the engine is off.
- Fusing: Each battery should have an inline fuse on its positive feed for safety.
Setup Tips: When wiring, always fuse close to the battery, and route cables to avoid hot or moving parts. Check that your 300 Series model doesn’t require any electrical tuning. Once installed, label which is the crank battery and which is the aux battery.
Choosing the Right Batteries: AGM vs Lithium
Selecting the right battery type is essential for a Landcruiser dual battery setup. The two most common options are AGM (Absorbent Glass Mat) and LiFePO4 (Lithium Iron Phosphate).
AGM batteries are maintenance-free, sealed, provide strong cold-crank amps, and tolerate engine-bay heat well. They are reliable for starting and moderate deep cycling but should not be discharged below around 50% to preserve lifespan. For example, in a recent 300 Series fitment, Batteries Sunshine Coast installed two heavy-duty PowerAGM dual-purpose batteries to deliver strong starting power and durability.
Lithium (LiFePO4) batteries are lighter, recharge faster, and offer 2–3 times the usable capacity of an AGM. They can be discharged up to 99% without damage, making them ideal for powering accessories overnight. However, they require a suitable DC-DC charging system and cost more upfront.
In summary:
- AGM Dual-Purpose: Good cranking power, sealed, low maintenance.
- AGM Deep Cycle: Best for accessories, moderate capacity.
- LiFePO4 Auxiliary: Light, high capacity, long life, ideal for off-grid use.
How a Landcruiser Dual Battery System Works
- Cranking Battery (Main) – Starts your engine.
- Auxiliary Battery (Secondary) – Runs your accessories when the engine is off.
- Battery Isolator / DC-DC Charger – Manages power flow, ensuring both batteries charge efficiently without draining each other.
When the vehicle starts, the alternator charges both batteries via the isolator or charger. When the engine stops, the isolator separates them — leaving your cranking battery fully charged for the next start.
Installation Considerations for the 300 Series
The 300 Series Landcruiser has some unique traits. The main battery is located under the bonnet on the passenger side (with a sealed cover), and space is tighter than older Cruisers.
- Mounting: Many dual battery kits are designed to fit under the factory cover. For example, a popular DIY kit uses the factory holes and fits entirely inside the engine bay with no visual change. You can either place the second battery next to or behind the first, depending on available room. Batteries Sunshine Coast notes that fitment restrictions in the new mount may limit battery height, so compact, slim batteries are safest.
- Under-Bonnet vs Rear: Most 300 Series installs keep both batteries under the bonnet. Some owners prefer to put an aux battery in the rear cargo area or under the seat, but this requires longer cables and more complex wiring. Under-hood keeps charging simple with shorter cable runs.
- Cabling: Use at least 4 or 6 gauge positive cables between batteries. Many dual battery kits include pre-terminated wiring harnesses for a clean install.
- Battery Cover: If you retain the stock battery cover, ensure the dual setup fits under it so the engine bay remains sealed. Many kits manage this by fitting the extra battery directly under the cover area.
- Heat: The engine bay can get hot. Ensure any lithium aux battery is rated for under-bonnet use, as not all lithium batteries are designed to withstand such temperatures.
- Cooling/Charging: The LC300 alternator is a powerful 200A non-smart unit, meaning it can handle heavy loads without cutting off early. The LC300 alternator handles most 12V setups well, but for very heavy power demands, consult a professional about upgrade options.
Always follow wiring diagrams and manufacturer instructions. If in doubt, have a professional (like Batteries Sunshine Coast’s workshop in Queensland) do the install. They recently performed a dual battery installation on a 300 Series, ensuring all connections were correct and tested. By comparison, an improper setup can lead to charging issues or electrical faults down the line.
Benefits of a Dual Battery System
To recap, a properly installed dual battery system on your Landcruiser 300 offers:
- Strong Engine Starts: You’ll have maximum cranking amps (CCA) from two batteries. In fact, one PowerCrank lithium unit provides 1600 CCA, and even two smaller AGM batteries can double cranking power.
- Extended Camping Power: Run fridges, lights, water pumps, and more for days. Use the aux battery for these loads while preserving the starter battery’s charge.
- Accessory Support: Operate radios, spotlights, winches, and other accessories without risk of draining both batteries at once. The aux battery picks up the slack.
- Redundancy: If one battery fails or is accidentally left on, the other can jump-start the vehicle. Batteries Sunshine Coast’s recommended kits often include a jumper-switch or fuse override for this scenario.
Owners on the Sunshine Coast and beyond trust local experts at Batteries Sunshine Coast to advise on the best dual battery components. We carry both the Stop Start batteries and high-performance lithium options needed for a reliable LandCruiser dual system. Local clients appreciate having service and battery warranties claims locally, and even roadside assistance if needed.
Installing Your Dual Battery System
Setting up a dual battery system in a Landcruiser 300 dual battery involves selecting the right batteries, securely mounting them, and connecting them using a DC-DC charger or isolator. A professional installer will typically use heavy-gauge cables and ensure all fuses or circuit breakers are correctly placed for safety. While DIY installation is possible, it’s essential to follow your kit’s wiring diagram carefully and double-check all connections. If you’re unsure, shops like Batteries Sunshine Coast can handle the full installation for you.
Maintenance Tips
Once your dual battery system is in place, maintain it as follows:
- Check connections periodically for corrosion or looseness. Clean battery terminals if needed.
- Monitor battery voltage: If you have a volt meter or battery monitor, keep an eye on the auxiliary battery’s state of charge. Don’t let either battery stay deeply discharged for long (especially AGM, which prefers not to go below ~50%).
- Top up or replace batteries: Most deep cycle batteries last 3–5 years depending on use. Rechargeable by solar or driving, but sometimes a little trickle charge (via a CTEK or similar) during long storage can preserve life.
- Inspect vents (if flooded battery): Some older battery boxes have vent tubes to outside; ensure they’re clear. Most modern units (AGM/Li) are sealed.
- Load-test start battery: If the engine starts to become sluggish, have the starting battery tested. It might be time for a new unit or a recharge.
A well-kept dual battery system means more trouble-free adventures and far fewer worries about electrical power.
Conclusion
Adding a dual battery system to your Toyota Landcruiser 300 Series is a smart upgrade for reliability and off-grid power. By carefully selecting the right batteries (AGM or LiFePO4) and using a proper isolator, you ensure your Cruiser can start its engine no matter what accessories you run at camp. This extensive 300 Series Landcruiser dual battery guide has covered why it’s valuable, how it works, and key installation points.
For personalized advice or fitting on the Sunshine Coast, the Batteries Sunshine Coast team can help. We carry all the recommended components – from heavy-duty PowerAGM batteries to high-output lithium units and Redarc chargers – and we know exactly how to install them in an LC300. Feel free to contact Batteries Sunshine Coast for help designing a Landcruiser 300 dual battery system that meets your needs, or for any battery service. Safe travels and happy camping!
Get Your Landcruiser 300 Series Dual Battery Installed Today
Whether you’re planning the ultimate touring rig or just want reliable backup power, a Landcruiser dual battery setup is one of the smartest upgrades you can make.
At Batteries Sunshine Coast, we specialise in 300 Series Landcruiser dual battery systems, including both AGM and lithium solutions tailored to your needs.
- Expert installation by qualified technicians
- Quality batteries with strong warranties
- Fast service — open Mon–Sat
Contact us today to book your installation or get expert advice on the right dual battery for your Toyota Landcruiser 300 Series.
Frequently Asked Questions
- Can I start my Landcruiser from the auxiliary battery?
Yes, if set up with a manual or automatic emergency link, you can jump-start your vehicle from the auxiliary battery. - Do I need a lithium battery for my 300 Series dual battery?
Not necessarily. AGM batteries are reliable and affordable. Lithium is ideal for weight savings, higher CCA, and longer battery life. - Can I run a fridge for days without draining my starting battery?
Yes — that’s the main benefit of a dual battery setup. The auxiliary battery powers your fridge, leaving the cranking battery fully charged.
