How To Install An Extra Battery For Car Audio System (With Diagram)

(Last Updated On: March 14, 2024)

Being a car owner, it’s likely that you are already aware that your car’s stereo impacts your car batteries. However, there is more to it, as sometimes, for enhanced audio and peak engine performance, the car audio system might necessitate the purchase of an additional battery.

In this article, we’d be taking you through the process of a car audio dual battery setup. We answer your most pressing questions using a step-by-step guide to installing the second battery for car audio with a diagram to walk you through the process. 

Car audio dual battery setup
Car audio dual battery setup

When To Add An Extra Battery For Car Audio

When Do I Need To Add An Extra Battery For Car Audio?

Barely 20 minutes into playing your favorite hop from your car stereo, only for it to go off because your car battery has gone flat.  That’s probably a sign you need an extra battery.

A simple hack to finding out whether you need a second battery is to check your headlights. If they’re dimming while using your audio, it’s a clear sign your amplifiers are using up more power than your battery and alternator can provide.

Generally, you need to add a second battery if you listen to your car audio with the engine off or have a powerful amplifier audio system.

How Long Can My Car Battery Last When The Engine Is Off?

A simple formula can help you determine the estimated length of time it will take for your battery to run your stereo with your engine off. It goes: 

Operating time = 10 X RC / Load

Where RC is battery reserve capacity (in amp-hours), the load is sustained. 

For example, if your car audio has a 700-watt load with a battery reserve capacity of 100 amps-hours, you’d have 10 X 100/700 = 1.4 hours to enjoy your car stereo. 

This is how adding a second battery helps to increase the battery reserve capacity and add to the operating time.

How To Choose An Extra Battery For Car Audio

Here are a few pointers to choose a second battery for your car audio: 

Determining Which Ratings Of Car Battery For Higher-performance Audio

Battery rating helps to show the amount of power a battery can prove, with reserve capacity and cranking amps as essential ratings. This allows you to compare different models and choose the most suitable option.

Reserve capacity (RC) refers to the amount of power a battery can provide over an extended period. This means a higher RC equals a more elevated and more extended battery power. On the other hand, cranking amps signal the battery’s amperage when it cranks the engine.

Choosing What Size Second Battery For Car Audio

Here, you’ll have to factor in the battery size and its reserve capacity. More often than not, the power to buy depends on the amount of power the amp needs. And a simple way to determine this is for every 1,000 watts RMS of your car audio system, you will need a 100Am battery. 

Installing New Matched Batteries

A common way to add an extra battery to your car is to replace the current battery with two matched batteries. Both replacement batteries must belong to the same age, group, and brand to get excellent performance.

Try the usual method of placing one battery precisely where the old battery was and wiring the second battery in parallel. By parallel,  this means you will connect the negative terminal on one battery to the second battery’s negative terminal. Do the same for the positive terminals. 

Read more:10 Best Car Batteries 2021 (Review and Buying Guide)

How To Install An Extra Battery For Car Audio (With Diagram)

So, now that you have your car battery ready, the next concern is how to set it up. 

Where To Place An Extra Battery For Car Audio

Where to set up dual battery for car audio
Where to set up dual battery for car audio. Credit:

More often than not, you will find your car batteries installed under a hood, so there is very little room left for a second battery in the same engine compartment. So, place your extra battery near the amplifier, either in the trunk or in the cabin. 

Leak-proof and vibration resistance are distinguishing features of batteries installed in the car. A standard lead-acid battery is a bad idea for car audio systems. The vibration resistance becomes important because installing a battery close to robust subwoofers means this battery would be receiving strong kicks from the subs. Similarly, mounting the battery in any spot other than the factory position or size makes the leak-proof super important.

Now you know where to place your second battery, let’s talk about how to set it up. 

Step-by-step Guide For Installing An Extra Battery For Car Audio

Extra battery for car audio system diagram
Extra battery for car audio system diagram

As stated earlier, parallel wiring is suitable when installing a second battery. 

Here’s a step by step guide to help you install a second battery for your audio using parallel wiring: 

  • The main car battery should be under your bonnet connected to your car and its peripheral such as aircon, headlight, etc. 
  • The second battery will be placed in the boot connected to the amplifier.
  • Remember, both the batteries need to be the same size, model, and age for the best efficiency. There are setups with different batteries, such as a smaller one at the front and a larger one at the back, and vice versa. Either way, you do it, you’re going to need to fuse three times. 
  • The first fuse of the main car battery will be within a foot of the battery. This fuse goes to the back of the boot, where the second battery is. There’s a fuse at that end within a foot of the second battery as well. 
  • The positive terminal of the second battery would go to your amp.  This would be fused within a foot of the second battery as well.
  • Make sure to ground the amp to the second battery. Of course, your primary car battery would already be grounded anyway, so you don’t need to worry about that.


  • Remember to have an excellent alternator to charge both batteries, or you might end up stranded somewhere.
  • Do not buy too large of a battery, or your alternator might not be able to keep up. But if you do have a large alternator, then all means get as big as batteries you can.

Read more: Bad Ground On Amp Symptoms


Can I use a regular battery for car audio?

Yes, you can. But take note that installing Lithium-ion batteries or higher output AGM will do more for your car audio system than regular lead-acid batteries. 

Do I need an extra battery for my subs?

Subs are the most potent parts of your car sound system, and you’d need an amplifier to power your subwoofers, even if you don’t have a strong one for speakers. 

For this, the subwoofers require a second battery, especially if it’s as powerful as thousands of watts. If you have a professional competition system installed, it’s crucial to ensure that systems receive the correct amount of energy. 

Read more: 1-Ohm vs. 2-Ohm vs. 4-Ohm Subwoofer: Which Is The Best?


Adding a second battery is not merely crucial to your car audio. It also determines the performance rate of the engine and, by extension, your car. Similarly, the size of the battery, where to place it, and how to install it are crucial questions to help you maximize your extra battery. You will find all the answers in this guide.

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