How to Fix a Car Stereo Draining Battery?


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?

As a general rule, before fixing a car stereo draining battery, you need to know if the stereo is old or newly installed. If the stereo is old, it can drain the battery due to a faulty relay. If a radio is newly installed, it is most likely wired to a fuse that receives power when the engine is off.

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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 Crenova 890Z. 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.

I will provide you with a straightforward guide to troubleshoot the problem and deduce where the issue is emanating through a process of elimination. 

How Can Car Stereo 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 your 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 My Battery?

There are possible three 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.

If the Problem Is 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 Stereo System

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.

Conclusion

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.

Martin

Welcome to ImproveCarAudio! I am Martin, and I love to write about everything related to car sound systems. I strive to provide the most accurate and helpful information about car audio through extensive research, as well as my experience with car audio installations.

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