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Can An Amplifier Drain Your Battery? (Car Amplifiers Tips)

Do you ever find yourself sitting in your car only to discover that the battery seems to be draining? Chances are if you’ve installed a car amplifier, it is pumping up your music with significantly more power than your standard sound system.

This power draw is coming from your battery, and if you don’t address why this is happening, it could mean that your battery ends up wholly drained and unusable.

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Car amplifiers can drain the battery in several cases:

#1. If the car engine is turned off.

#2. If the alternator cannot charge the battery faster than the car audio system requires.

#3. The amplifier has a faulty ground connection or loose wiring.

#4. The amp is connected straight to the battery without a remote wire going to the stereo.

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

Tip: Factory car batteries are not always designed to handle powerful amplifiers. To maximize your car audio system’s performance, check out the best car batteries and charging accessories on

In the article below, I will detail the causes of car battery drains and show you how to fix this problem.

Does a Car Need Battery?

The role of the battery in a car is to start an engine, and when the engine does not run, the battery supplies electricity to AC, lights, radio, and other car equipment.

Unlike many people think, a car battery does not produce energy, but it stores and supplies the car’s electrical equipment with the energy produced by an alternator.

Alternator, when the engine is running, supplies a car with needed electricity and charges the battery at the same time.

Modern cars can run without batteries if they have a solid alternator to support all electrical equipment.

car amplifier drain a battery

The only thing you cannot do without a battery is to start the engine with the key or push button. You can, however, try pushing a car to make it start from the hill, but you need to have a manual transmission to do it.

Set a second gear, and your car will run OK after a few yards of pushing. But let’s come back to the main topic of this article, and talk about batteries.

What Does It Mean When a Car Battery Is Drained?

When you try to start an engine, and after turning a key, you hear nothing or just a weak sound of a starter motor for a second or less, your battery is likely dead.

It could also be a broken starter motor, but in 99% of cases, when you cannot start an engine, the reason is a drained battery.

It happened to me many times, especially in the ’90s, when I was driving my first cars with second-hand batteries, loose alternator belts, etc.

The engine cannot start because your battery does not have enough energy to run a starter, and there are several reasons for the battery being drained:

#1. You have a powerful sound system with a standard alternator, or the alternator itself is damaged

#2. Car equipment consumes too much energy when the engine is not working. For example, when you leave lights overnight or listen to music for a long time.

#3. The acid level in the battery is too low, or your battery terminals are tarnished.

Can Car Audio System Be Too Strong for a Car Battery?

It is a common question when problems with batteries start to appear after installing a strong amplifier.

The capacities of factory-mounted batteries are designed to fit a particular car with standard equipment. However, adding additional amplifiers increases electrical system requirements, depending on the amplifier power.

To calculate the exact amperage for your amplifier, you have to divide the total RMS of your amp (not per channel) by 13.8V.

The table below shows the amperage for the car amplifiers. I used for this example efficiency of 70%:

Amplifier RMS (Watt)Amperage needed if the amplifier was 100% efficientReal amperage needed (at 70% efficiency)

The table shows how high amperage must be supported by car alternators and standard car equipment.

If your total amperage demand in a car exceeds what the car’s alternator can produce, even the most durable battery will die because it always has to support an alternator.

The alternator will never charge it unless you turn the radio off, and power demand will drop.

When looking at the battery label, you will see two important symbols with numbers behind them. It is worth remembering what they mean.

#1. Ah – Ampere Hours means how many hours your battery can supply your car with 12V power.

For example, the battery Ah65 can continuously provide 1amp for 65 hours or 10amps for 6.5 hours until it is fully discharged. After that time, you will have a dead battery.

#2. CCA – Cold Cranking Amps mean how many amps your battery can deliver consistently for 30 seconds in temperature 0°F until voltage drops below 7.2V.

The table below shows popular conversions between CCA and Ah and how powerful amplifiers you can connect to your battery without further modifications.

Battery CCABattery AhMax amplifier RMS

From the above, you see how powerful an amplifier you can install in your car without facing any later issues with the drained battery.

For example, when you have a standard car battery CCA710, you will be OK with a 650W amp, but for a 900W amplifier, this battery is a no-go, and you may need to install a secondary battery to power the aftermarket amplifier.

If you listen to music nonstop while driving, the battery will never be charged by the stock alternator, and it is a matter of time before it will eventually die.

Strong amplifiers may not only cause drained batteries, but you may also notice dimming headlights or flickering dash lights.

Also, it can happen that the amp will not receive full power, so your bass will be weak.

How to Keep Amp From Draining Battery?

When you have a powerful amplifier, or more than one, and to make sure that your battery will never drain because of the car audio, you have to consider replacing an alternator with the powerful one.

This way, you will be able to supply enough energy for your car’s audio system, and at the same time, your battery will always be charged.

car audio alternator

A few years ago, I replaced my wife’s car’s standard amplifier with Mechman 370A, which works great.

I have had no problem with batteries since then, and she uses a relatively powerful Rockville RXH-F5 with 1600W RMS. (link to Amazon opens in the new window).

The high output alternator cost me over $500, which is expensive. Still, it balances out when I put this price against risking often battery replacement and time for a regular charging battery at home.

Typical alternators mounted in an average passenger car can produce between 80 – 120A depending on the model.

This 80A will support around 660W RMS from the amplifier, and if you do not have more power, you do not need a stronger alternator.

But what will happen when you add a 2000W amplifier to your car for a subwoofer?

This is an additional over 100A, which a standard amplifier cannot produce. Many people went through this many times, and the effect was always the same.

When you listen to music, mainly when the engine is on, adding a powerful alternator is the only solution to keep your battery in good condition and the whole system without energy shortage.

Before you start making electrical changes in your car, you need to know if this is really necessary, especially when your amplifier is not the most powerful, so its power consumption should be supported by standard car equipment. The best way to find out is to test both a battery and an alternator.

How Do I Stop My Amp From Draining My Battery?

There are several ways to prevent your amplifier from draining your battery.

Here are a few simple tips to help you conserve battery power:

#1. Make sure the amplifier has a remote wire connected to the car radio that turns off your amplifier when it’s not in use.

This is the most obvious and effective way to conserve battery power, preventing the amp from running when it should not.

#2. Use a battery with a higher capacity. This will give you more power to work with and help your amplifier run more efficiently.

However, you may need to upgrade the alternator to ensure the larger battery is adequately charged.

By following these tips, you should be able to conserve battery power and keep your amplifier running for a longer period of time. Remember, it’s always best to conserve energy whenever possible and be mindful of how much power your amplifier uses.

How to Test Battery and Alternator?

Testing the battery voltage and alternator charging quality is the best way to determine how healthy both are.

You need a voltmeter and no more than 5 minutes of your time to perform the test.

how to test a car audio battery

You will also need someone to start your engine while you make a test, and you can do the whole test at home. I am using Crenova MS8233D digital meter, which does a great job.

Before the test, ensure both battery terminals are clean and without corrosion. If you notice corrosion on the terminals, you need to clean them.

Take the leads off and clean using sandpaper, then when clean, put them back together.

I use it for cleaning sandpaper grids 100 or 120, and it works well. After that, spray both with a WD40. This will prevent terminals from getting rusty.

Check alternator wires for any corrosion if they sit well in the pockets. Also, check if the alternator belt is tight, and if it is not, this will cause a problem while charging a battery.

#1. Turn headlights on and run it for around 2 minutes

#2. Do not turn a radio on, or anything else in a car

#3. Set the voltmeter to value over 12V DC. Depending on the model, it can be 16 or 20V.

#4. Connect a red voltmeter wire with the positive battery terminal

#5. Connect a black voltmeter wire with the negative battery terminal (ground)

#6. Read the value on the voltmeter. For a good battery, you should see over 12.4V, in most cases closer to 13V.

#7. Do not unplug the voltmeter and start the engine. During start value on the voltmeter should drop to around 10V and then jump right back to over 13V.

Test Results

When you start an engine and the voltage drops below 10V, your battery is weak. And if it drops below 6V, your battery is dead and needs to be replaced.

If your engine works and you see voltage always between 13.2V and 14.7V, that means the alternator is in good condition and is charging system. In this case, you have nothing to worry about, and both parts work great.

The next step is to turn your electrical equipment on, including lights, AC, fan, and car radio.

The value on the voltmeter should drop to over 13V. If you see over 13V with your car audio on, your alternator and battery are in excellent condition.

But, if you see a voltage below 12.7V, that means an alternator does not produce much power for the demanding equipment in your car and does not charge a battery at the same time. In this case, you should replace an alternator.

How to Stop Amp Draining Car Battery When Off?

When you have powerful amplifiers in your car, you must know that even if the engine is off, these can still cause a battery to drain if the amp is not connected to the stereo via a remote wire.

What Is a Remote Wire?

A remote wire is used to switch the power on or off for your amplifier. 

When connected, the head unit sends the signal to the amp, which will be powered when the key is in the ignition.

When turned off, this wire will switch the amp power, preventing any current drain from happening when you are not using your audio system.

Will a Capacitor Keep My Battery From Dying?

A car capacitor, also known as a power or audio capacitor, can potentially help prevent a car battery from dying in the short term, but it is not a guaranteed solution.

Here are a few points to consider:

#1. A car capacitor stores electrical energy and releases it quickly when needed, which can help with power-hungry car amplifiers.

#2. If a car audio system is causing the car battery to drain quickly, adding a capacitor can help to smooth out the power demand and reduce the load on the battery.

However, a capacitor will not recharge a dead battery. Therefore, if the battery is old and weak, it will still need to be replaced.

A capacitor will also not help if the battery is dying due to other issues, such as an alternator that is not working correctly or a parasitic drain on the battery.

Therefore, it is important to diagnose the root cause of the battery drain before deciding to add a capacitor.


In conclusion, if you want to know why your car amplifier drains your battery, you should perform a series of tests.

First, make sure both terminals are clean and without corrosion.

Then measure the voltage with the voltmeter before starting an engine.

Finally, start an engine and check the value on the voltmeter. If it drops below 10V, you need a new battery, as the existing one is dead.

If you see a voltage below 12.7V with electrical equipment on, the load on the alternator is high, and it should be investigated further. In some cases, the alternator will have to be replaced.

If the voltage is between 13.2V and 14.7V, your alternator is in good condition and is charging your battery correctly.


Do I Need a Capacitor for My Car Audio?

Adding a capacitor helps to stabilize voltage in a car.

This is especially important for powerful car audio systems, where together with loud bass, you notice dimming headlights. An amplifier and battery cannot handle such a spike in energy demand, so an external capacitor is needed.

This article will give you more information about car audio capacitors, which ones to use, and how to connect them.

Do I Need an Extra Battery for Car Audio?

Adding a second car battery works only when you listen to music with the engine turned off.

Depending on the amplifier’s power draw, an extra battery can extend the listening time from a few minutes to another hour.

When the additional battery is connected in parallel between the original one and the amplifier, the whole system works exactly like a standard battery but with extra capacity.

To know more about additional batteries for car audio, read this article.

Why Is My Amplifier Draining My Car Battery When It’s Not in Use?

Your amplifier can drain the battery when it is not used, for example, when it has a “standby” or “idle” mode that still uses power, even when it’s not actively playing music.

Another possibility could be an issue with the amplifier’s power switch, waht may cause it to stay on even when you think it’s off.

It’s also possible that there’s a problem with the wiring or installation of the amplifier that is causing a short circuit.

What Should I Check if My Amplifier Is Draining My Car Battery?

Most importantly, you should check the remote connection to the stereo and make sure when the radio turns off, the amp also stops working.

I also recommend checking for any loose or corroded connections in the wiring, which could be causing a short circuit.

Additionally, you can check for any signs of damage or wear on the amplifier itself, such as a broken power switch or an overheated component.

Can a Faulty Alternator Cause My Amplifier to Drain My Car Battery?

A faulty alternator can cause the battery to drain because it will not charge it correctly, but it does not cause immediate problems with the amplifier.

However, it’s always good to check the alternator and battery voltage to make sure they’re working correctly, in case it might be the root cause.