The Original Retailer of True® Dual Smart Battery Isolator

Step-by-Step DIY: How to Install a 12V Dual Battery System in Toyota Prado Using True® Isolator Kit

 

Installing a 12V dual battery system in your Toyota Prado is one of the best upgrades for off-road adventures, camping, and powering accessories. With a True® battery isolator kit, you can safely run fridges, lights, and electronics without risking your starter battery.

This step-by-step DIY guide will walk you through the entire installation process—from preparation to final testing.

 

Why Install a Dual Battery System in Your Toyota Prado?

A dual battery setup allows your vehicle to:

  • Power accessories without draining the starter battery
  • Ensure reliable engine starting at all times
  • Support off-grid travel and camping setups
  • Improve electrical efficiency with controlled charging

A properly installed isolator ensures the auxiliary battery only charges when the engine is running and disconnects when the engine is off, preventing battery drain.

Tools & Materials Needed

Before starting, gather the following:

  • True® battery isolator kit (12V)
  • Deep-cycle auxiliary battery (AGM or lithium)
  • Battery tray (Prado-specific)
  • 4–6 AWG battery cables
  • Fuse holders and fuses (50A–150A)
  • Cable lugs and heat shrink
  • Crimping tool and wrench set
  • Multimeter
  • Protective gloves and safety glasses

 

 

 

Below is a Step-by-Step DIY Guide Tailored for the 2024 Prado:

Step 1: Safety First

Always start by disconnecting the negative terminal of your starter battery to avoid short circuits or electrical damage

Make sure:

  • Engine is off
  • Vehicle is in park
  • No sparks or open flames nearby

 

 

 

Step 2: Install the Auxiliary Battery

Mount the auxiliary battery in a secure location:

  • Under the hood (if space allows)
  • Rear cargo area with a battery box

Ensure:

  • Proper ventilation
  • Heat protection
  • Firm mounting using a battery tray

 

Step 3: Mount the True® Battery Isolator

Install the True® isolator close to the starter battery:

  • Keep it away from extreme heat (engine/exhaust)
  • Use vibration-resistant mounting points
  • Maintain short cable runs for efficiency

Mounting near the battery improves performance and reduces voltage drop

 

 

Step 4: Install Circuit Protection (Fuses)

Install fuses on both batteries:

  • One near the starter battery positive terminal
  • One near the auxiliary battery

This protects your system from short circuits and electrical faults

 

⚖️ Comparison: True® Dual Battery Kit vs. Basic Relay Setup

 

FeatureTrue® Dual Kit (with DC‑DC charger)Basic Voltage-Sensing Relay
Works with Smart Alternators✅ Yes❌ No
Starter Battery Protection✅ Always preserved⚠️ Risk of drain
Fuse & Cable Safety✅ 40–60A matched to 4 AWG❌ Often undersized
Battery Options✅ AGM & Lithium supported⚠️ Limited
OEM Integration✅ CAN bus compatible❌ Not supported

 

Step 5: Wire the System

Main Connections:

  1. Starter Battery → Isolator Input
  2. Isolator Output → Auxiliary Battery Positive
  3. Auxiliary Battery Negative → Chassis Ground

Use heavy-duty cables (4–6 AWG) for efficient power transfer.

 

Step 6: Grounding

Proper grounding is critical:

  • Connect both batteries to a solid chassis ground
  • Clean contact points to ensure good conductivity
  • Use thick ground cables equal to positive cables

Poor grounding can cause voltage drops and system failure

Step 7: Optional Accessories Wiring

Once the dual battery is installed, connect accessories to the auxiliary battery only, such as:

  • 12V fridge
  • LED lights
  • USB chargers
  • Inverters

This ensures your starter battery remains untouched

Step 8: Reconnect & Test

Reconnect the starter battery negative terminal and test:

  1. Start the engine
  2. Check voltage at both batteries
  3. Confirm isolator engages (charging both batteries)
  4. Turn off engine and ensure isolator disconnects

A properly functioning isolator will:

  • Charge both batteries when running
  • Isolate them when off

 

 

Step 9: Final Inspection

Before hitting the road, check:

  • Tight cable connections
  • Secure mounting
  • Proper fuse placement
  • No exposed wires

 

Pro Tips for Toyota Prado Owners

  • Newer Prado models (150/250) may benefit from a DC-DC charger, but isolator kits like True® still work effectively for many setups
  • Use AGM batteries for under-hood installs due to heat resistance
  • Upgrade to thicker cables if running high-load devices

 

Conclusion

Installing a True® dual battery isolator kit in your Toyota Prado is a practical and rewarding DIY project. With the right setup, you’ll enjoy reliable power for all your accessories while keeping your starter battery fully protected.

Whether you’re heading off-road, camping, or working remotely, this upgrade ensures your Prado is always ready to go.

DFNA