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Why Car Amplifier Drains Your Battery And How to Fix It?

Many people complain that after installing car audio their subwoofer killed a car battery, but is this problem really caused by a subwoofer?

I did some research to find out if a car amplifier can drain your battery, and the results are quite interesting.

So, can an amplifier drain your battery? The simple answer is yes, but a car battery can only be drained when it sends more power than receives back from an alternator. In other words, a car battery drains when it is not charged enough, which is a common problem when using powerful amplifiers. Also, the amplifier will drain the battery when is connected straight to the battery, without a remote wire going to the stereo. In this case, the amplifier will drain the car battery, even when the engine is turned off.

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. If you want to maximize your car audio system’s performance, check out the best car batteries and charging accessories on now.

Let’s find out what it means and how to fix this common problem.

Why 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.

Cars can run without batteries if they have a strong alternator to support all electrical equipment.

car amplifier drain a battery

You just cannot start the engine without a battery. 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 after a few yards, your car will be running OK.

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, most likely your battery is 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:

  • You have a powerful audio system with a standard alternator, or the alternator itself is damaged
  • Car equipment consumes too much energy when the engine is not working. For example, when you left lights overnight or listened to music for a long time
  • The water level in the battery is too low, or your battery terminals are tarnished

Is My Car Audio System Too Powerful for my battery?

It is a common question when, after installing a strong amplifier, problems with batteries start to appear. The capacities of factory-mounted batteries are designed to fit a particular car with standard equipment. By adding additional amplifiers, you increase 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 has to be supported by car alternators, in addition to the standard car equipment.

If your total amperage demand in a car exceeds what your alternator is capable of producing, even the most durable battery will be dead because it always has to support an alternator. In effect, it will never be charged unless you will turn a radio on, 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.

  • Ah – Ampere Hours, that means for how many hours, your battery can supply your car with 12V power. For example, battery Ah65 can continuously provide 1amp for 65 hours or 10amps for 6.5 hours until is fully discharged.
  • CCA – Cold Cranking Amps mean how many amps your battery can deliver consistently for 30 seconds in temperature 0°F until voltage will drop 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. Assuming that 40% of the battery amperage powers car equipment, and the remaining 60% you can use for car audio amplifier.

Battery CCABattery AhMax amplifier RMS

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

For example, when you have a car battery CCA710, you will be OK with a 650W amp, but for a 900W amplifier, this battery is a no-go.

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

Strong amplifiers do not only cause drained batteries but also you may 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 an Amplifier from Draining Battery?

car audio alternator

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.

A few months ago, I replaced in my wife’s car standard amplifier with Mechman 370A, and it works great. I have had no problem with batteries since then, and she is using a quite powerful Rockville RXH-F5 with 1600W RMS. (link to Amazon opens in the new window)

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

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 simply cannot produce. Many people went through this many times, and the effect was always the same.

A brand new battery was installed, and with a standard alternator after a few weeks or months, the battery was gone, and the process of regular daily recharging at home begins. This is not the way I want to go, I want to have in a car enough power to support my car audio.

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 to Test Battery And Alternator?

how to test a car audio battery

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

To perform the test, you need a voltmeter and no more than 5 minutes of your time, you will also need someone to start your engine while you make a test and the whole test can be done at home. I am using Crenova MS8233D digital meter and I am happy with it.

Before the test, make sure 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.

  • Turn headlights on and run it for around 2 minutes
  • Do not turn a radio on, or anything else in a car
  • Set the voltmeter to value over 12V DC. Depending on the model, it can be 16 or 20V.
  • Connect a red voltmeter wire with the positive battery terminal
  • Connect a black voltmeter wire with the negative battery terminal (ground)
  • Read the value on the voltmeter, for the good battery, you should see over 12.4V, in most cases closer to 13V.
  • 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 voltage drops below 10V, that means your battery is weak. And if 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 the battery. In this case, you have nothing to worry about, both parts are working great.

  • The next step is to turn your electrical equipment on, lights, AC, fan, 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 enough power for the demanding equipment in your car and does not charge a battery at the same time. In this case, an alternator should be replaced.

Related Questions

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.

In this article, you will find 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 the music with the engine turned off. Extra battery, depending on the amplifier’s power consumption, can extend the listening time from a few minutes to another hour.

When the additional battery is connected in parallel between an original one and 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.