If you are into car audio, I’m sure you’ve heard the phrase: “It takes power, to make power” and for car audio systems, this is so true. In order for your car audio system to perform at its peak, it needs some serious juice, and your stock electrical system definitely isn’t up to this task.

In such a case, you have a few options to consider. One, you can upgrade your stock alternator with a high-output unit, which I have discussed in a previous post, here. Second, you can replace the OEM battery with the biggest AGM equivalent you can fit in the stock location, or thirdly, you can add a secondary battery into the mix.

Swapping the alternator is a great choice, and it is one you should consider doing, but the alternator is only working when the vehicle is running. Changing out the OEM battery can also be very beneficial, but you may not have the reserve capacity available to be demoing your system for prolonged periods of time with your engine off. 

This is why, in this post, I will discuss how to install a secondary battery (AGM for this post) and the benefits of doing so. For my examples, I will be referring to a 2002 Chevrolet Silverado 2500 HD because this was the most recent dual-battery install that I was a part of and I’m sure a lot of truck guys may be wondering how it is done with such limited space.

For some, installing a secondary battery for a car audio system can be an anxiety-inducing process for those who are not comfortable with their vehicle’s electrical system, but stick with me. You’ll see that installing a secondary battery in your car or truck can be a simple task, especially if you’ve already tackled doing a BIG 3 upgrade on your vehicle. If you haven’t, you can learn how to in my previous post on installing a BIG 3.

Before we get started with the complete install, we should look at what you need in order to do a proper and complete installation. Here are some of the items you may need:

Now that you have an idea of what you may need to get your install rolling, let’s begin the process of installing our battery set up.

Table of Contents ( EZ Sort)

The Installation

The first, and probably most important decision to make is where to install the secondary battery. This will differ based on the vehicle, but in the 2002 Silverado, I chose the passenger side of the engine bay (behind the coolant overflow bottle) for the location. This is where you can sometimes find a secondary factory battery, but in the case of my installation, there was no pre-installed battery there.

The first step for me was to install the battery tray. I purchased a plastic battery tray from a local auto parts store. Next, I installed the battery into the tray and strapped it down, making sure it was firmly in place and secure. No matter the vehicle, you want to make sure the battery is secure and will not move around or tip over within the engine bay, passenger compartment, or trunk. 

After the battery is in its final location, it is time to run the cables needed to connect the two batteries together. For this install, it may be important to note that I also replaced the primary battery, with a matching AGM. This is not necessary, but for this installation, I chose to go this route.

To run the cables, I loosely set the cables in their approximate location running from the primary battery, along the top of the radiator, then around the fuse box to a fuse holder, then an isolator, another fuse holder, and then to the second battery. Once the approximate length and layout were determined, I cut the cables to length and crimped on some good quality copper lugs, and added heat shrink over the lugs. Next, I installed the loom onto the wire to aid in protecting it, plus it keeps the wiring looking like the OEM wiring throughout the engine bay. 

The reason I used an isolator in this install was to limit either of the batteries from draining each other should the charge level on either drop below a certain point. Some will say you don’t have to run an isolator, but I always do. You can learn more about isolators and separators, here. 

Once all of the wiring is taken care of, it is time to connect the two batteries. In this case, you need to pay special attention to how the wiring is done. In order to keep the power supply at 12 volts, you will need to wire the two batteries in parallel. This means positive to positive and negative to negative. Wiring in parallel will double your amperage and reserve capacity but will keep the voltage safely at, or within, the 12-volt range. 

If the batteries are wired in series, then you can kiss all of your electronics goodbye, or set your truck on fire. This not only doubles the amperage and capacity, but it will also send 24 volts through your entire truck’s electrical system, so pay attention here. 

Also, a good practice is to ground both of your batteries to the truck’s chassis. Some people like to skip this step on the secondary battery, thinking that having it connected to the primary battery and then the primary battery being grounded to the chassis is good enough, which it can suffice, but why not beef up your grounds by grounding the second battery to the chassis as well? Your electrical system is only as good as the grounds, so save yourself the grief, and do it now. 

Once the two batteries have been connected and you have checked everything for correctness, i.e. voltage, grounds, connections, you are good to run the wiring from your secondary battery to your amplifier(s). Don’t forget to fuse this wiring as well. 

Once everything is all wired up and safe from rubbing on things, or moving parts, you can fire up your car audio system and demo to your heart’s content.


It is my hope that this post on adding a secondary battery to your vehicle has given your some basic knowledge and understanding of how to perform this installation. With a little bit of planning and insight, adding another battery to your system can be an easy task to perform. And, the process, whatever the vehicle, will be similar

NOTE: I would recommend that you have, at least, some basic knowledge of how a vehicle’s 12-volt system works and some basic wiring knowledge before tackling this installation. If you are, at all, hesitant or feel you lack the necessary knowledge, I would seek help from a professional in this case. Safety of yourself, and your vehicle should be your top priority.

How To Install a Second Car Audio Battery In Your Vehicle!

About The Author Brandon L

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