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How to Wire Multiple Batteries for Car Audio?

As car audio systems have become increasingly powerful, the need for more than one battery to power the system has also increased.

Additional batteries can help to increase the overall performance of the car audio system by providing more power and smoother voltage delivery.

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When additional batteries are needed for car audio, it is essential to connect them correctly, but how to connect multiple batteries for car audio? Let’s find out.

When connecting multiple batteries for car audio together, you have to wire them in parallel. This means that the positive terminal of one battery is connected to the positive terminal of the other battery, and the negative terminal of one battery is connected to the negative terminal of the other battery. The parallel connection of multi batteries keeps the voltage the same but increases the capacity.

As an Amazon Associate, ImproveCarAudio will receive a small commission from qualifying purchases made through the links in this article.

Tip: When connecting additional batteries for car audio, use the same gauge for all wires.

The gauge depends on the system, but since you are wiring multiple batteries, I am assuming the total power of your amplifiers is over 5,000W. In this case, you should use good quality 0 AWG wires, and those that I use are from KnuKonzeptz. (link to Amazon)

In this article, I will cover everything you need to know about wiring multiple batteries for car audio. Also, I will explain when an additional battery is required for car audio and how the battery helps overall car audio performance.

Will Adding a Second Battery Help My Audio System?

Adding a second battery is a good idea if you want to run the car audio system longer when the engine is off, but an additional battery will not improve performance when the engine is running.

When the engine is running, the better solution is to upgrade the alternator to a larger one.

The reason for this is that car audio systems are limited mainly by the amount of power they can draw from the electrical system and not by the amount of battery capacity.

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An additional car battery also helps reduce the voltage drop when the car audio system plays at high volumes, especially when you use powerful subwoofers.

In this case, the additional battery works similarly to a car audio capacitor by storing and releasing electrical energy very quickly.

When Should I Add a Second Battery to My Car Audio System?

installing an additional car battery is recommended if you want to:

#1. Run the car audio system for a long time when the engine is off.

#2. Improve car audio system performance by reducing voltage drop.

#3. Use car audio system at high volumes.

In other words, an additional battery is unnecessary if you have one amplifier for the speakers and do not use strong subwoofers.

Should I Connect Batteries in Series or Parallel?

Any additional car battery should be connected to the main battery in parallel.

Do not connect car batteries in series because the series connection summarizes the voltage and does not increases the capacity.

Connecting car batteries in series will not improve car audio system performance and may even damage the amplifiers.

If you want to increase the voltage of your car audio system, you can use a voltage converter or a voltage booster, but this is the case only when you, for example, use a 12V battery in an 18V or 24V system.

How Do You Install Multiple Batteries?

Installing multiple batteries is not difficult, but there are a few things you need to consider, and the main one is safety.

By safety, I mean you should put fuses on all positive witing between the batteries, not only between the battery and the amplifier.

This is important because if there is a short circuit in the car audio system, the fused car battery will be protected from damage or even explosion.

Another thing to consider when installing multiple batteries is that you should use the same type of battery in the same condition as the existing one unless you install all brand new batteries in the car.

Before starting, make sure that the car audio system is turned off and all wires are disconnected from the amplifiers.

#1. Disconnect the negative terminal of the first battery.

#2. Connect the positive terminal of the first battery to the positive terminal of the second battery.

#3. Connect the first battery’s negative terminal to the second battery’s negative terminal.

If you have more batteries, you must follow the same sequence and connect the positive terminals first and then the negative terminals.

Once all batteries are connected, you can reconnect the first battery’s negative terminal. Now your car audio system is ready to use with multiple batteries.

One last thing you should do is to check the voltage of the additional batteries using a voltmeter (link to Amazon).

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Because you made the parallel connection, the voltage should be the same as the first battery. If it is not, then there is a problem with the connection, and you have to recheck it.

How to Charge Multiple Car Batteries?

Charging multiple car batteries is not difficult, and you can use the same charger as for a single battery.

The batteries in car should be charged in parallel, however, to charge connected batteries together, they have to be identical.

To do this right, connect all positive terminals for all batteries and also all negative terminals together. Then connect the charger to one of the car batteries, and it will start charging all batteries at once.

Since all batteries are connected in parallel, it does not matter to which one you will plug the charger.

If you want to charge batteries that are not connected with each other, connect the charger to one battery at a time.

Do I Need a Bigger Alternator for Two Batteries?

The size of the alternator does not need to be changed when you install additional car batteries because the car audio system will not draw more power from the alternator.

However, to maintain good charging for all connected batteries, you should keep an eye on the voltage drop.

If the car audio system is drawing too much power and the alternator can not keep up with the demand, you may need to upgrade the alternator to a larger one.

Do I Need an Isolator for a Second Battery?

If you want to use the car audio system and the additional car battery only when the car engine is running, then you don’t need an isolator.

The car battery will charge itself while driving, and the alternator will power the car audio system.

However, if you want to use the car audio system even when the car engine is not running, you need an isolator (link to Amazon).

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An isolator is a device that prevents the main car battery from being drained when the car engine is not running and is often used in car audio systems that do not have separate battery circuits.

This is because, without an isolator, the main car battery will be slowly drained when in the same circuit with other batteries, and at some point, it will not have enough power to crank the car engine.


Adding an additional car battery is an excellent way to improve the car audio system’s performance. One thing to remember is to use the same battery as the main one and to connect them in parallel.

If you want to use the car audio system even when the car engine is not running, then you need an isolator.

You also need to keep an eye on the voltage drop when using multiple batteries and, if necessary, upgrade to a bigger alternator.