How To Wire A Dual Battery System

Installing a dual battery setup in your vehicle is a great way to power additional accessories without draining your main starting battery. And with a dual battery system, you essentially have separate batteries for engine starting and accessories.

So what’s the benefit? Well, this setup provides extended battery life, more power for add-ons like lights and refrigerators, and redundancy if one battery fails. In this post, I’ll walk through the complete process for wiring a dual battery system.

Step-By-Step Process to Wire a Dual Battery System

Step 1:

The first step is choosing compatible dual battery systems. For the starting battery, stick with the type recommended by your vehicle’s manufacturer, usually a standard flooded lead-acid battery. 

For the auxiliary battery, you have more flexibility. Popular options include absorbed glass mat (AGM) batteries and lithium-ion batteries. AGM batteries are spill-proof and mount in any orientation, while lithium batteries are lighter, charge faster, and have a longer lifespan.

Just make sure the auxiliary battery’s voltage matches your starting battery. Unless your starting battery is lithium, opting for an AGM auxiliary battery is a safe bet.

Step 2:

Once you have the batteries, it’s time to install the key component – the battery isolator. This device connects both batteries while preventing them from discharging each other. We recommend installing the isolator near the starting battery to minimise cable length.

Follow the specific wiring diagram for your isolator, connecting the start battery’s positive lead on one side and the auxiliary battery’s positive lead on the other.

Step 3:

Now you can mount the auxiliary battery. Place it in a protected area away from heat and moving parts. Make sure it’s properly ventilated if using a lead-acid style. Use mounting hardware designed for automotive batteries to prevent cracks and spills. 

Step 4:

With the battery mounted securely, connect the negative lead to the vehicle’s chassis or body, not the starting battery.

Step 5:

Double-check your connections, then connect the two positive terminals to the isolator. I recommend installing fuses here to protect the system from shorts. A 200 amp ANL fuse should suffice for most setups.

Step 6:

The final step is wiring your accessories like lights, refrigerators, or power outlets. Run the positive accessory wires to the auxiliary battery’s positive terminal and ground the negatives. If adding multiple accessories, use a fuse block or terminal bus bar to consolidate the connections.

Final Note

That covers the basics of installing a dual battery setup! 

Taking the time to wire it correctly will ensure your accessories have ample power without compromising your starting system.

If you’re not sure what battery system you need to ensure the best possible setup for your needs, contact our team today for helpful advice.