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How to Fix Car Stereo Draining Battery? (Tips to Avoid Battery Drain)

There is nothing better than having a car stereo system that sounds crisp and produces a perfect audio output.

But sometimes, your stereo system may begin drawing on your car’s battery parasitically, causing it to drain and die. So, how do you fix a car stereo which is draining your battery?

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#1. Double-check all the wiring and connections to ensure they’re secure and not damaged.

#2. Ensure the stereo’s automatic power-off feature is functioning correctly.

#3. Turn off unnecessary features like the display or lights when not in use to conserve battery power.

#4. Consider installing a battery-saver device to prevent the battery from draining when the car is not in use.

#5. If you’re not using the car, disconnect the battery or install a battery disconnect switch.

#6. If the problem persists, have a professional look at the stereo to diagnose and fix any underlying issues.

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Tip: If your car radio drains the battery, the first thing I would do, is to test all wiring connections.

My favorite digital multimeter that I have found excellent for this purpose is the AstroAI TRMS 6000. The best thing is that it can measure all electric parameters, and it will help you analyze potential problems that may arise with your car audio system.

In this article, I will go over the most likely scenarios for causing your car’s stereo to drain the battery and will recommend possible solutions for each of these.

How Can Head Unit Drain Your Car’s Battery?

The term “parasitic draw” refers to an electrical component in your car that is drawing amperage from the battery when it shouldn’t be. 

This causes your battery to become overworked and drained and can result in a completely dead battery. In this case, the stereo is the parasite, drawing energy away from the battery, leaving it drained and unable to work.

There are several ways to tell if a battery is drained. The most obvious is that your car will have trouble starting up. It will show an abnormally struggled and excessive cranking sound when trying to start the engine.

Some of the other signs that your battery is suffering from a parasitic drain are:

  • Dimmed lights, especially the headlights.
  • The check battery light is being indicated on your dashboard.
  • Your car backfires.
  • The car won’t turn over unless you give it gas.

A car’s battery provides the ignition with the initial power to start. But once your engine is running, most of the energy used to supply the internal electrical components is derived from the alternator.

Your vehicle’s stereo system should never put an excessive drain on your battery. If it does, then there’s a problem.

You will also want to keep in mind that if your car’s engine is off, but the battery is turned on, and you are using the car’s electrical features, such as the stereo, the heater/A/C, or the lights, it will drain car battery at a fast rate.

While the battery can directly power the stereo for a brief while with the engine off, it is not designed to do this for a long time, and it will eventually die.

A car battery’s primary function is to provide the car with enough energy to start and passively assist the alternator while the engine is running.

If you are sitting in your car with the engine off but the stereo’s on, make sure you turn on the car every once in a while. This will prevent the battery from dying.

As a side note, it is worth mentioning that although I specifically focus on discussing the causes of a stereo that is draining your battery, sometimes batteries get old in general and should be replaced.

As a rule of thumb, your car’s battery should ideally be replaced with a new one every three years. Beyond this, they can begin to rust, corrode, become weakened, and you run the risk of getting stranded. 

Car batteries are relatively inexpensive and well worth the investment. If your current battery is weak, the new one will significantly improve your vehicle’s performance.

Why Is My Car Stereo Draining Battery?

There are three possible scenarios that are concerning your stereo and the drain it is inflicting upon your car’s battery:

  • A new stereo has been improperly installed.
  • Your old stereo is ready to be replaced.
  • Your stereo system is too powerful, and the battery cannot keep up.

A New Stereo

You’ll know if it’s the first scenario where you’ve just installed a new stereo system in your car because the issues will present immediately after the installation.

In that case, the problem is probably either that your radio was not wired correctly or that your car’s battery and alternator do not have enough power output to accommodate the new stereo system.

An Old Stereo

In the second scenario, chances are you have had the same stereo for a long time, which probably came installed directly from the manufacturer.

In this case, the issues may present seemingly out of nowhere, draining your battery for no apparent reason. In this instance, it is more than likely an issue with the stereo itself, and it may be time for a replacement.

The Stereo is Too Powerful

In this case, you may have opted for larger speakers and maybe even a bass speaker to make your music pop. Unfortunately, such modifications are too much for certain cars to handle. You may find that your speakers are drawing too much power, taking away from the battery’s primary function.

Below, I will expand on each of these scenarios in further detail and go over some quick and easy solutions.

Note: If you are new to and uncomfortable working with cars, it may be advisable to seek a trained automotive professional rather than attempting to troubleshoot the issue yourself. Always work safely and work within your scope of knowledge and ability.

How to Fix Problems With the Wiring?

In this scenario, you have most likely just installed a new stereo system in your car or vehicle only to realize that it is drawing on your car’s battery parasitically.

If you have done the wiring yourself, then you may have overlooked a factor somewhere. As a result, the improper wiring setup is causing your stereo to function unintended and finally draining the battery.

When you purchase a new stereo system, it should come with a guide on how to wire the system correctly to avoid problems with a flat battery. However, every car and stereo is different, and the instructions may not have been clear or adequate.

If you have read the wiring instructions from the stereo system’s manufacturer and cannot understand what is causing the problem, it can leave you scratching your head in confusion but do not worry. There may be a straightforward solution to this problem, and resolve may take no more than a few minutes.

Check the Fuse Terminal (Constant vs. Switched Fuse)

In every car you will find a fuse box, and each of its fuse ports typically serves one of two functions. Some of the ports on your fuse box are constant, while others are switched:

  • Constant fuses are ports that are powered at all times, even when the car’s engine is off.
  • Switched fuses, on the contrary, only receive power when the engine is running.

If you have accidentally attached your stereo to a constant fuse, it may continuously draw power from the battery while your car is not running. This will put undue demand on your battery and cause it to drain down, resulting in a struggling turn-over when you start the vehicle.

Your stereo should be wired up to a switch fuse.

The Solution

Every brand and model of car will have a slightly different fuse box arrangement. There is only one way to be sure which fuses are constant and switched: you must manually test them.

You will need a voltage continuity and current testing device to perform this task. Thankfully testers are not too expensive, and the one I can recommend is the Katzco Current Tester for its ease of use and reliability.

To test your fuses, follow the steps below:

  • Turn off your vehicle’s engine, remove the key, and find the fuse box.
  • Locate an unpainted and bare metal surface on your vehicle and ground your current tester to this point (clamp onto this metal surface with the alligator clip on the wire of the tester, opposite the sickle-like end of the device.) VERY IMPORTANT!
  • Begin testing the fuses by probing them with your device one at a time. 
  • The constant fuses will light up your device while the car’s engine is off, and your stereo should not be hooked up to any of these terminals.

While the fuses which did not light up during this process are likely switched fuses, you can confirm this by turning the car’s engine on and testing these ports once more to prove. This should resolve the wiring problem and eliminate the battery drain.

If you have any concerns about the efficiency of your current tester, you can test its performance and functionality simply by hooking the ground clip to the negative (—) terminal on your car’s battery and touching the probe to the positive (+) terminal.

If your tester is in working order, doing this should cause it to light up and indicate the presence of a live current.

If the Problem Is With the Stereo Itself

If your car stereo suddenly begins sapping your battery out of nowhere, despite not being a newly installed system, you can almost certainly rule out a wiring problem. In this scenario, you are most likely looking at an internal issue within the stereo itself.

Car stereos work via a complex series of relays which are sent through their internal circuit boards. This is how the stereo can do what you tell it to do.

For example, when you turn the unit on and off at the press of a button. Think of this circuit board as the brain of your stereo.

As your car’s stereo ages and gets old, some of these relay pathways can get worn out, stuck, or stop working how they should for one reason or another.

This can create a situation where your stereo is not going to sleep when it should. Something is still drawing power from within the stereo when it is not supposed to be, and in the end, this will of course, drain your battery.

Even if everything looks to be in working order with your stereo and it acts and behaves as if it is in excellent shape, there may still be something within the unit that is malfunctioning in some way that is undetectable during regular use.

So, what can you do with a stereo system that is draining your battery because of an internal relay glitch?

The Solution

Unfortunately, if one of the relays has gone within your car’s stereo, it is probably not worth trying to repair as this process can be very complex and not worth the time and effort.

It can be complicated, if not impossible, to accurately determine the exact relay causing the problem as there are many possibilities for where the problem can happen.

Furthermore, even if you find the issue, there is very little you can do in the way of physical repairs to solve the problem.

In many cases, the best you can actually do is to replace the old stereo with a new one. Doing so will fix this problem immediately. Just be sure to avoid the fuse hookup mistake when installing your new unit.

In the meanwhile, disconnect the stereo to prevent it from draining down your battery.

If Your Battery/Alternator Is Not Equipped To Handle Your Car Audio

The third and final reason that your stereo system might be draining your car’s battery is that the system may be too powerful for the battery or the alternator in your vehicle. It may also be demanding more amperage from them than they can accommodate.

This third scenario will only be relevant to those who have seriously high-powered sound systems with many amplifiers and is unlikely to happen with a typical car stereo.

Stereo systems use whatever excess power is left over from the alternator to operate. If your stereo requires too much power from the alternator, the latter will have trouble recharging the battery while the engine is running, and this may produce a draining effect.

This effect is known as “outrunning,” which means that your stereo is outrunning the battery, and the alternator cannot keep up with charging it back.

The Solution

The solution to the problem of your stereo outrunning your battery can either be simple or complicated, depending on who you ask.

The typical remedy for this issue is to either upgrade to a bigger battery or, better yet, add an auxiliary (second) battery into the car to accommodate for the extra output.

Upgrade Your Battery

Upgrading to a bigger battery can be a hassle because the battery might physically be too big to fit in your car’s tray.

Instead, it will need to be mounted in the trunk, requiring you to rework many things around to make this possible. In general, however, as long as the bigger battery has the correct voltage, it will not cause any harm to your car.

Install a Second Battery

When your sound system is really powerful, the better bet is to go the route of setting up a second battery.

A second battery also has the advantage of being able to be used continuously while your car’s engine is turned off. Upgrading to a larger battery does not grant this option, as it will still die the way any single battery would.

A second battery or even more than one is a usual modification for vehicles with heavy electrical components like tow trucks, RV’s, and race cars.

Having a second battery exclusively designated for powering your stereo system will ensure that the unit has all of the power it needs and will not compromise the main battery and, in turn, the functionality of your vehicle’s performance. This eliminates the chance of you getting stranded somewhere as the result of a dead battery.

If you decide to install another battery, it should always be wired in parallel with your first (primary) battery.

A common suggestion among people who run a dual battery setup in their vehicle is to buy a matching pair of brand-new batteries. While this is not a mandatory rule, I prefer this solution because hooking a new battery up to an old one, especially if the existing battery is not in the best condition, may not produce the most optimal result.

This process is not as complicated as it may sound, but it does guarantee an entire write-up on its own because it requires a fair bit of understanding.

Thankfully, this article by MTX Audio provides a comprehensive walkthrough of this process, so if your stereo needs more juice, check it out!

If you have read through the process and are still unsure, you should take your vehicle to the service, preferably one specializing in specialty sound systems, and have the replacement done.

It is not worth taking risks that may cause damage to your vehicle.


It turns out there are three situations that will cause the stereo to drain the battery.

  • The stereo may be wired to a constant fuse port that receives power even when the car is off – switching to a switched fuse will fix this.
  • An old stereo might have a circuit board fault. In this case, it is not worth fixing, and you should seek a replacement.
  • Lastly, the stereo may be too powerful for the alternator. Consider wiring in a second battery for more power.


Why Does Car Stereo Drain Battery Even When The Car Is Off?

This could be caused by a malfunctioning head unit or amplifier or a faulty wiring connection.

Also, often car stereo drains the battery because it is in standby mode and uses a small amount of power to keep its memory alive.

Constant radio connection to the battery on a standby mode is known as a “parasitic draw,” and it can slowly drain your car’s battery over time.

One way to check is to remove the fuse for the stereo and see if the battery drain stops. If it does, then the issue is likely with the stereo system.

What Can I Do to Prevent My Car Stereo From Draining the Battery When the Car Is Off?

One solution is to install a battery disconnect switch, which allows you to quickly disconnect power to the stereo system when the car is not in use. 

Additionally, make sure that the radio is correctly installed and grounded to prevent power leakage.

How Can I Tell if an Aftermarket Car Stereo Is Causing the Battery Drain?

Try disconnecting the aftermarket stereo and see if the battery drain stops.

If it does, then the problem is likely with the stereo. Also, check the wiring and all the connections to ensure they are secure and not corroded.

Why Does the Battery Keep Dying, Even Though I Just Replaced It?

It could be that the alternator is not working correctly and not charging the battery while the car is running.

It could also be a problem with the battery, such as a short or a malfunctioning voltage regulator.

Why the Battery Drains Quickly Even When I Am Using the Car?

When the battery drains while the car runs, it is most likely because of the malfunctioning alternator.

Why Did the Battery Die After Installing Aftermarket Radio?

If you have installed a new aftermarket car stereo and find that your battery is dying, the main reason for this is incorrect wiring to the car battery or the faulty electronic in the radio itself.

Can the Stereo Drain Battery While the Car Is Running?

The car stereo cannot drain the battery while the car is running. This is because the radio takes power from the alternator while a vehicle runs. 

An alternator also recharges the battery as it is used.

If the radio drains the battery while you drive, there is probably a problem with how it is installed or with the alternator itself.

Can Radio Memory Drain Car Battery?

When the car is turned off, the radio goes into standby mode and uses a small amount of power to keep its memory alive.

This is a “parasitic draw” and is slowly battery over time.

To fix this problem, you can disconnect the battery from the car stereo every time you do not use it, but by doing this, the radio will reset each time you disconnect it from the power source.

How to Stop Radio From Draining Car Battery?

If your car radio is draining your car battery, you should check the installation to ensure that all the wires are correctly connected.

Another way to prevent the battery from draining is disconnecting it when you are not using the car stereo.

This will prevent the radio from going into standby mode and using power to keep its memory alive.

Would Improperly Connected Car Radio Cause Battery Drain?

Incorrectly connected car radios may cause battery drain and damage the head unit or other parts of the car’s electrical system.

Can a Radio Fuse Drain a Car Battery?

A fuse cannot drain a battery, but if a car radio is not wired correctly, it could cause a fuse to blow.

What Is Car Radio Parasitic Draw?

A parasitic draw is when a small amount of power is used to keep something alive, even when it’s not in use.

In the case of car radios, a parasitic draw happens when the radio goes into standby mode and uses a small amount of power to keep its memory alive.

Can a Bad Ground Cause a Parasitic Draw?

A bad ground can cause a parasitic draw. For example, if the ground wire is not connected correctly, it can cause the car stereo to use more power than it should.

A bad ground can also create an alternative path for the electricity and, in effect, cause a short circuit.

Does Having the Car on Accessory Kill the Battery?

Leaving a car on the “accessory” mode allows drawing a limited amount of electricity to run certain accessories, like the radio, the power windows, and the interior lights.

If the car is left in the accessory mode for many hours, the running radio or lights can slowly drain the battery.

In some car models, the car will automatically turn off the accessories after a certain time to prevent the car battery from being drained.

Can Aftermarket Radio Cause Electrical Problems in Cars?

Any radio installed incorrectly can cause car electrical problems. If aftermarket radio is not grounded correctly, it can cause static electricity build-up and eventually a short circuit.

An improperly wired car stereo can also draw too much power from the car battery, causing it to drain.