How to wire multiple batteries for car audio?

We all love playing music in our car audio system. Listening to a song or radio may not seem a problem when driving the car. When you park your car and try to play your car audio, you may end up with a drained-up battery. 


You can’t start the ignition of your vehicle then, do you? You may have faced this many times. Have you ever wondered why it is happening? 


It looks like your battery can not supply enough power to play the audio and start the engine. So, you may be thinking about how to wire multiple batteries for car audio

Why would you need extra batteries for car audio?

Car batteries generally produce power to start up your vehicle’s ignition, automatic doors, air conditioning system, car speakers, and much more. So when you are thinking about listening to your favorite song or radio channel, you should consider the power your battery generates.


Generally, your car has an alternator that charges your car battery when the engine is running. So, when you are driving your vehicle, you don’t need to think about the power your car audio system needs. 


But when your car isn’t moving, the alternator stops charging the battery up. So, you can see now why you can’t play music when your car is in the parking lot.

Single battery vs multiple batteries: Which one to choose?

Most of the time, one single battery isn’t enough for a car if you want to play your car’s sound system. You’ll need an auxiliary battery to support your main battery. 


Sometimes, you may need multiple batteries depending on your vehicle’s need. So, you need secondary car batteries for accessories like listening to the radio, opening windows, etc., when the main battery can only focus on generating the engine’s power. 


Now the question arises: How should I use extra batteries for my car audio? We’ll get you right into that.

How to choose multiple batteries for car audio?

When choosing batteries for your car, you should be concerned about the ratings of the batteries that the company provides. You should keep your eyes on the “Cranking amps” and “Reserve capacity” of a battery. 


These are the most important ratings for a car battery. Cranking amps measure how much current or voltage the battery should provide when the engine is cranked. The battery reserves capacity refers to its ability to hold a specific amount of charge for a certain period.

What size second battery for car audio should I buy?

The size of the second battery is also significant. If you have enough space for a bigger battery to install, you should choose the bigger one. The bigger battery has the best reserve capacity. 


But if you are in a tight situation considering the space for a second battery, go with a smaller one. In case you are thinking of using two new batteries, you need to stick with us.

Installing a pair of new matched batteries for your car audio system

When you are thinking about installing two new batteries for better performance, you should be concerned about the sizes, weights, groups, and brands. Always select the same group and brand batteries. 


Because you don’t want one battery to produce less or more voltage than the other one. If possible, install the same charge-leveled batteries. Because if you insert two different charged batteries, one may have been overworked while another may have still been unused. 


It will force one battery to pull the juice out of the other battery, which will shorten their lifespan.

Installing a secondary battery with the existing battery:

If you are on a tight budget or not thinking about changing the main battery, you have to choose a battery that is identical to the original battery. You don’t need to panic if you can’t find an exact match because you’ll need an isolator in this installation. 


An isolator isolates your primary battery power consumption from other ones. It also helps the alternator charge the auxiliary battery only. So you don’t need to worry about draining up your main battery, as your second battery will start working when your engine is off.

Battery connection types: Which one is the best type of battery? 

There are two ways to connect your batteries: parallel connection and series connection. When you are wiring two new batteries, you should connect those parallelly. 


Parallel wiring simply implies that each battery’s terminals are connected identically: positive to positive and negative to negative. You may connect the batteries in a series as well. 


But connecting batteries in series may cause the first battery to overheat. The other problem is that the power is not evenly spread amongst the batteries, leading one battery to do overwork. 


This is why you need to use an isolator to isolate the main battery from other batteries. Using a parallel connection in a dual battery system is helpful to save power.

How to install a second battery for car audio? Step by step guideline

Getting new batteries in your car might not be easy. You don’t want to end up with failure when wiring new batteries. Besides, the electrical system can be dangerous. So you need a proper guide to error-free installation. Here are some tips on how to run 2 batteries for car audio:

Step 1: Unplug the wires from the battery

Start unplugging the power wire from the starter battery. You may see some red and black cables most of the time. If not, be sure which one is negative cable and which one is positive. You need to unplug the negative wire first. 


You will see that the battery’s positive cable is connected with a connector. Unplug or cut this at the alternator’s end.


Step 2: Add a high output alternator

If it seems that your existing battery alternator is insufficient to charge up both the batteries, you need to change the alternator. Pick a high output alternator if it supports the capacity of your battery and engine. Now connect the alternator at the exact same place as the previous one.

Step 3: Attach an isolator

To attach a battery isolator, take the positive wire of the starting battery and connect it to the left terminal of the isolator. The cable which came from the alternator should go with the right terminal of the isolator. Connect a more extended power wire with the middle terminal of the isolator to connect the auxiliary battery to its positive terminal.

Step 4: Connect the negative cable

Now connect the negative cable from your primary battery to the auxiliary battery.

Step 5: Grounding both batteries

You should connect both the batteries to the chassis or the same ground spot. You simply need to attach a cable(ground wire) to the second battery’s negative terminal to the chassis or anywhere to the ground.

Step 6: Connect the amplifier

The last step is to connect your sound system amplifier to the battery. Connect a red 4-gauge wire to the positive terminal of the secondary battery and run it to an amplifier fuse. Finally, connect a second red wire to the amplifier from the fuse.

Things to remember while wiring multiple batteries

  • About voltage drop. Voltage drop happens when using cheap battery cables. Try to use heavy gauge cables.
  • About any shortage or spark from the battery terminal. Use plastic caps to reduce the risk.
  • About any drilling you want to make. Make sure you don’t compromise your fuel tank or any essential parts of the car.

How to wire 3 batteries in a car?

In some cases, your car may need more than a dual battery setup to function properly. Well, if you are thinking about wiring 3 batteries in your car, you just need to follow the steps mentioned above. 


But you will need a more powerful alternator and more modified isolator to get this done. First, connect the alternator to the modified isolator. 


Now from the isolator, connect the batteries to their positive terminal. After that, connect the negative cable of each battery to their negative terminal and ground it to the chassis.


In the end, we can say that you’ll need an extra battery for the car audio system if you want to hear a song while parking or when you go for a picnic. But merely inserting a secondary battery kit for car audio would harm your car battery if you just plan to play music on a drive. 


Extra battery adds more pressure on the alternator. Battery and capacitor charge maintenance is the primary goal of an alternator. It provides continuous power to all electrical components.


So, the alternator must work harder to keep up with the increased demand for batteries. You need an extra battery to reserve power to play music or radio when the car remains idle. But a capacitor is an easy solution if you want to put on some music while driving. 


  • Do you really need a battery isolator?

Yes, you need one if you are thinking of installing a 2nd battery. Because without an isolator, your dual battery system will work as a unified system. This will cause faster battery drainage. So if you use a battery isolator, you can play a song while reserving the power of the main battery.

  • Can I use a regular car battery as a second battery for car audio?

If you like to play music all the time, a second battery can come in handy. Using a regular battery is safe. But you need to ensure your secondary battery produces enough voltage to keep you entertained. You don’t need to own a car audio battery; the regular battery would do the work.


  • Can you run two batteries with one alternator?

Yes, you can. When you use two batteries on an alternator, it takes them as a single unit and starts charging them. This means you can run multiple batteries on a single alternator.

  • How to wire two batteries for car audio?

You need to wire two batteries through a cable to each battery’s positive terminal, which will connect the isolator or alternator. After that, you need to connect the negative cable to the batteries’ negative terminal, which will go straight down to the chassis. Now you can connect your car audio amplifier, and that’s it.

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