Installing a dual battery setup in your vehicle is a great way to power additional accessories without draining your main starting battery. With a dual battery system, you essentially have separate batteries for engine starting and accessories, giving you more power, longer battery life, and redundancy if one battery fails.

Here’s a step-by-step guide to wiring a dual battery system:

Step 1: Choose Compatible Dual Battery Systems

For the starting battery, stick with the type recommended by your vehicle manufacturer, usually a standard lead-acid battery. For the auxiliary battery, you have more flexibility — popular options include AGM batteries and lithium batteries. AGM batteries are spill-proof and mount in any orientation, while lithium batteries are lighter, charge faster, and have a longer lifespan. Ensure the auxiliary battery’s voltage matches that of your starting battery.

Step 2: Install the Battery Isolator

The battery isolator connects both batteries while preventing them from discharging each other. We recommend installing the isolator near the starting battery to minimise cable length. Check out our Redarc Smart Start SBI isolators for reliable, high-quality options. Connect the starting battery’s positive lead on one side and the auxiliary battery’s positive lead on the other.

Step 3: Mount the Auxiliary Battery

Place the auxiliary battery in a protected area away from heat and moving parts. Ensure proper ventilation if using a lead-acid battery. Secure it using automotive-grade battery mounts and trays to prevent movement, cracks, or spills.

Step 4: Connect the Negative Lead

Attach the auxiliary battery’s negative lead to the vehicle chassis or body — not the starting battery. This ensures a stable ground connection.

Step 5: Connect Positive Terminals & Fuse Protection

Connect the positive terminals of both batteries to the isolator. Install a fuse here to protect the system from short circuits — a 200 amp ANL fuse is usually sufficient. Explore our range of fuses and fuse holders to keep your system safe.

Step 6: Wire Your Accessories

Connect accessories like lights, refrigerators, or power outlets to the auxiliary battery’s positive terminal. Ground the negatives. If installing multiple accessories, a fuse block or terminal bus bar helps consolidate connections neatly.

 

Final Note

Taking the time to wire your dual battery system correctly ensures your accessories have reliable power without compromising your starting system.

Not sure which battery setup is right for your vehicle? Contact our team today for expert advice and check out our full range of dual battery kits to get started!