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Car Audio Capacitor Vs. Battery: Which Should You Install?

There’s no denying that high-end aftermarket car audio system require a ton of power. And If your car’s electrical system isn’t able to keep up with the increased power demand, you’ll experience a wide variety of problems including flickering or dimming headlights, voltage drops, amplifier cutting out ..etc.

This usually happens only in large, multiple-kilowatt sound systems. But sometimes even modestly powered systems can increase the strain being put on your vehicle’s electrical charging system. This is especially true during a sub amp’s burst of energy when it produces the sound of the beat.

There are a few actions you can take to give your car’s electrical system a power-up. Adding an extra battery or a car audio capacitor seems more logical and efficient. However, there’s some strong and differing opinions about which is best to use, and even their individual usefulness. The following is our contribution to the argument.


It must be noted that factory wiring for the most part is thin and insufficient for running anything but basic audio systems. Therefore, performing what is known as the “Big Three” wiring upgrade should be the very first upgrade you make to your electrical system before adding additional batteries, capacitors, or alternators.

Big 3 upgrade refers to replacing or augmenting three key cables in the electrical system with larger diameter (thickest gauge) wires (such as 1/0 or 4 gauge wires): the battery ground to chassis wire, the chassis to engine block wire, and the alternator plus to the positive terminal of the battery.

Performing this upgrade will increase your electrical system’s current flow capability, ensuring a more consistent and stabilized voltage supply under varying demand conditions. And as a result, it’ll allow you to add more powerful audio system components down the line.

Car Audio Capacitor

A capacitor, or cap, sometimes also called stiffening cap, is an electronic component that stores up electrical energy, then releases it to your amplifier during peak demand for more consistent bass.

Car audio capacitors are meant to sit between your amp and your car’s electrical system to smooth out the power demands by providing the immediate jolt of power your amp needs on those dragged out loud bass notes, thereby preventing the car’s lights from dimming.

A capacitor will not by any means improve your system’s low end response and overall sound. However, it does make it easier for the amp to perform its best, and helps prevent the sound from deteriorating due to under-voltage.

As far as cap size is concerned, the general rule of thumb is to use 1 Farad of capacitance for every 1,000 watts RMS of total amplifier power. You can also use larger value capacitors. The larger the cap, the more electrical power is available for the amp when it needs it.

When to Add a Capacitor?

Adding a car audio capacitor to your electrical system will not by any means increase your system’s power capacity. However, if your headlights dim only occasionally, and only when heavy bass notes hit, then a capacitor may be just what you need. It’ll keep more of a constant voltage and smooth out the power demands by providing a short burst of energy when needed.

Car Audio Battery

Whether you need a second battery for your car audio system is determined by your setup, and what you’re into.

Adding a second battery is a good idea if you want to be able to run your car audio system for extended periods of time with the engine being turned off. However, this won’t do you any good when the engine is actually running.

So, if you’re into car audio competition for example, or if you spend a lot of time tailgating or dry camping, then a second battery is definitely a must. In those cases, you’ll typically want to install one or more deep cycle batteries.

Unlike regular car batteries, deep cycle batteries are designed to be regularly deeply discharged using most of their capacity without being damaged. That means you can use your electronic devices all you want without any fear of damaging your battery.

The idea is to use the original battery when you’re driving, and the bigger deep cycle battery when you’re parked.

This has the added advantage of preventing the risk of running a battery flat, and leaving you stranded in the middle of nowhere.

A second deep cycle battery should be wired in parallel with your original battery. However, it’s recommended that you use an isolator between the two batteries, so that the one used to start the car won’t get drained by the amp’s pull.

In other words, you’ll want the batteries setup in such a way that when you’re parked, you only draw power from the deep cycle battery, and when your engine is running, you’ll want to have to option to isolate the deep cycle battery from the charging system.

When to add a second battery?

As we’ve mentioned above, adding a second battery makes total sense when running the car stereo for extended periods of time.

An extra battery is also essential if you want your vehicle to run a heavy electrical load, without being left with a dead starter battery.

It’s also a must for systems with such a large power draw, and systems where the demand for electrical energy slightly exceeds the output of the alternator.

Car Audio Capacitor Vs.  Extra Battery – Which is best?

There are a number of key factors to consider when deciding between a car audio capacitor or second battery, from your own setup and what you’re into to the nature of problems your stereo system is experiencing. Here’s what you need to know before buying either one.

In a nutshell, a battery offers the amperage you need to properly power your amplifier(s), while a capacitor helps with regulating the voltage so that your amplifier(s) are constantly being provided with the required voltage (14.4V), which will allow your amps to run more efficiently.

That said, a capacitor should be added when you’re experiencing dimming headlights when bass hits hard. While a second battery should be added mainly if you spend a lot of time tailgating or dry camping or if you spend a lot of time listening to music with the engine turned off.

So, it’s not a matter of which is best but which is more practical for your needs.

Do you really need to add an extra power source to your system?

The original electrical system in most vehicles is designed and built for the stock features. It isn’t powerful enough to provide the necessary juice to run power-hungry aftermarket audio equipment.

Adding beefy amps and subs to your stereo system increases the strain on your electrical system. This leads to a wide variety of problems including bothersome headlight dimming, slow power windows, or amplifier cutting out when the car-audio system is booming…etc.

So, unless you’re experiencing any of the above issues, there’s no need to consider adding a cap or a second battery.

Generally speaking, car audio systems with less than 1,000 watts RMS of total output rarely, if ever, need the vehicle’s electrical system upgraded.

Alex Brown

Hey There, my name is Alex Brown, I'm an LA-based sound engineer with over 10 years experience installing, troubleshooting, and repairing commercial, automotive, and household sound equipment. I've installed highly competitive car audio systems, and everything from navigation systems to full car stereo systems, remote starters, alarms and beyond. I enjoy creating solutions and simplifying everyday needs. I also love helping people get great sounding gear, thereby, saving the world from bad sound one customer at a time.

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