How To Install A Dual Battery System In A Vehicle

Installing an entertainment system in your car is good for the soul. As health experts always insist, some good music is perfect for your general health. Unfortunately, your only car battery can’t handle the power load of a high-end system. So, what can you do in case you want a robust system in your ride?

The best option is usually to install a second battery in the car, which deals with the extra load. The secondary battery should be powerful enough to keep the stereo running. That means that you will continue enjoying your music without draining your primary battery. Surprisingly, most drivers don’t know how to install a dual battery system in a vehicle.

Ways to Add A Dual Battery System to Your Car

Well, the installation process can be a bit tricky for the first-timers as it calls for some wiring and modifications. Therefore, if you’re new to the world of vehicles, you should let a professional handle the installation on your behalf. But, if you’re a DIY kind of a guy, here is a step-by-step procedure on how to perform the modifications or you can watch this helpful YouTube video below:

What Tools Do I Require?

• Second battery
• Drill and bits
• Multimeter
• Crimping tool
• Voltage-sensitive relay
• Marker pen
• Connecting wires
• Battery tray and straps
• Pliers
• Dual battery kit

Once you’re ready with these tools, you can proceed to perform the modifications.

1. Position the Second Battery

Your first and most significant step should be to find a perfect location to hook the auxiliary battery. You can find some space within the engine area and fix the new battery. If your battery happens to be large, you can as well fix it in the trunk. The trunk area does work well, especially when the battery is to be used to power an audio system.

In case you use the trunk, you must ensure that you have enough wires to reach the second battery. Also, you must ensure that the second battery is tightly-held in position as that is going to be its new home. It’s at this point that the battery tray comes in the picture to help hold the battery in place.

The tray works super fine because it can be screwed to your trunk while you strap the battery to it. It helps reduces the unnecessary vibrations that can lead to damages on your just-installed battery.

2. Disconnect the Primary Battery

Before you start working on any wiring and stuff, you should remember to unplug the main battery first. The step helps prevent any shorts that may arise from the battery being connected.

3. Position the Voltage-Sensitive Relay (VSR)

Remember, the idea behind a dual battery system is to have two batteries in one car, performing different tasks. Here, you need the primary battery to stick to its work, which is starting the car. On the other end, the auxiliary battery is tasked with powering the accessories even when the vehicle is off.

It’s at this point that a VSR is needed to ensure that the two batteries work accordingly. The component allows the primary battery to start charging when the car starts moving. When the battery is full, the part engages the secondary battery so that it can also get some charge. The VSR works similarly when the car is switched off. It disengages the primary battery to ensure that you use the secondary battery.

Therefore, you will need to mount the VSR, preferably somewhere close to the main battery. You can locate a place around the engine area, away from the heat and moving parts. The tool can be screwed to a substantial component in your vehicle, within the engine area.

4. Connect the Positive Terminal of Your Primary Cell to the VSR

Once the VSR is held in position, your next step should be to connect it to the positive terminal of the main battery. You need first to measure the length of cable required to run from the tool to the main battery. When measuring the distance, always follow the existing paths to avoid bumping into hot or moving parts within the engine area. The wire from the main battery should be attached to the VSR terminal with a red dot.

5. Repeat the Same Procedure With the Second Battery

Now that the primary cell is connected to the VSR, next, you should work on connecting the positive terminal of the additional battery to the VSR. The cable from your secondary battery should be attached to the mark labeled as the positive second battery on the VSR plate.

6. Earth the VSR

Your next move should be to connect the VSR earth. When it comes to earthling the VSR, you must ensure that the earths are grounded correctly. You can go ahead and use a bolt that hasn’t been used to earth any component within the engine area.

7. Earth the Auxiliary Battery

The additional battery does require earth, as well. Therefore, you can go ahead and attach the black cable to solid ground within the engine area or the trunk.

8. Attach the Negative Leads

Once the secondary battery is earth, go ahead and secure the negative points. First, begin with the main battery then to the second battery. You should ensure that your wiring is neat for the sake of working on them in the future if they develop a problem.

9. Test Your Dual System

After you’re done with all the wiring and stuff, it’s time to test if the whole thing is working. This is where a multimeter comes in to help. You should start the engine and take the reading from your primary battery.

If the system is wired correctly, you should hear a clicking sound of the VSR whenever the battery’s voltage goes beyond 13.3 volts. A red light should also illuminate to show that a second battery is attached. If you observe that, it means that you’ve succeeded in modifying your battery system, and you’re set to go.


Having two batteries in a car is beneficial, as it means you will never experience cases of a flat battery. Besides, it allows one to utilize the entertainment features installed in the vehicle without any worries. In this article, you will find a step-by-step guide you can follow to install the dual battery system to your vehicle. Read through the entire piece to understand how easy it’s to perform the task.

1. Installing a Dual Battery Kit – Supercheap Auto Australia
2. The ultimate guide to dual-battery system – CarsGuide
3. Workshop: Dual-battery systems – SA 4×4
4. Dual battery systems explained – WhichCar