What Drains Your Car Battery the Most? Top Culprits You NEED To Know!

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What Drains Your Car Battery the Most

Your car battery is under attack. What Drains Your Car Battery the Most and how can you stop it? Read our article and find out.

Nothing is more frustrating than getting into your car and finding out that it won’t start. You turn the key, but nothing happens. You check the battery, but it’s dead. How did this happen? What drains your car battery the most? The answer is that a drained battery can be caused by the alternator or charging system. Various components can also cause a drained battery. But that’s not the whole story.

Many factors can affect your battery’s health and performance. These factors include the weather, the age, and the usage of your battery. In this post, I’ll explain the top culprits that drain your car battery the most.

Read on to find out more.

Key Takeaways

  • A drained battery can be caused by the alternator or charging system. Various devices can also cause a drained battery.
  • Frequent use of power-hungry features like windows may drain the battery.
  • Battery maintenance and weather can both significantly affect battery life.
Appliance/PartApproximate Amperage Draw
Alternator or charging system0.1 to 0.3 amps
Lights (interior and exterior)0.5 to 2 amps
Radio or entertainment system0.5 to 5 amps
Ignition system (spark plugs, distributor, etc.)3 to 6 amps
Fuel pump3 to 10 amps
Heater and blower motor10 to 20 amps
Power windows and seats3 to 20 amps
Air conditioning system15 to 30 amps
Starter motor50 to 200 amps
Parasitic draw from aftermarket accessories or modificationsvaries widely
Old or failing batterycan vary depending on the condition of the battery
Short trips or infrequent drivingcan vary depending on the length and frequency of the trips

Source: Your Mechanic / Battery University

Alternator or Charging System

Did you know your car’s alternator plays a big role in keeping your battery charged?

That’s right. The alternator is the heart of the charging system. While you’re driving, it recharges the battery and powers the electrical systems. So, if there’s a problem with the alternator, it can affect the battery’s charge.

For instance, a loose belt in the charging system may stop the alternator from working correctly. Then, you’ve guessed it, the battery loses its charge.

Another issue could be a worn-out tensioner. It can hinder the alternator’s performance if it affects the belt tension. If the belt is too loose, it can start to slip and cause the alternator to undercharge the battery.

Moreover, an alternator with a bad diode can drain your battery. Interestingly, this can happen even when the engine is turned off, so your car might not start in the morning after you left it overnight.

And that’s not all!

A bad diode can sometimes cause the alternator to overheat, killing your electrical components. Bad news, right?

Lights and Radio

Electrical systems are a big cause of battery drain; let me talk you through some of the potential pitfalls.

Interior and Exterior Lights

Let me tell you, one of the biggest culprits of battery drain is our car lights. Sometimes, we forget to turn off the headlights or leave the interior lights on. That’s plain and simple human error and can deplete the battery.

Yes, most modern vehicles have a failsafe ensuring that lights turn off, but if one fails, you might have a problem on your hands.

Car batteries also power exterior lights, like on your side mirrors or door lights. So, if you forget to shut a door or the trunk all the way, these lights may stay on. They will keep draining the battery overnight. This will leave your car struggling in the morning.

That being said, the type of bulb also makes a difference. Traditional incandescent bulbs drain the battery faster than LEDs, which use relatively little power.

Radio or Entertainment System

Ever notice how your car radio keeps on playing even when the engine is off? That’s because the battery keeps it alive. But it can’t do so forever. The longer you play your radio without the engine running, the more it drains the battery.

You would think that newer cars would avoid this issue. But even they can have charging problems if the alternator isn’t working properly. The alternator’s job is to recharge the battery while the engine is running. And if it doesn’t do so, a rogue stereo can be all it needs to nix the battery.

So, when enjoying your favorite tunes on a road trip, make sure to run the engine regularly. It will give the battery a chance to recharge. This will keep your car running and keep the music playing.

Ignition System

But we can’t talk about car batteries without mentioning the ignition system, can we?

Well, quite.

The ignition system is the heart of the car. Amongst other things, it includes spark plugs and the distributor. They work together to start the car and keep it running.

But how can it drain the battery? Let’s take a look

The Ignition Switch

The ignition switch is a vital part of your car’s ignition system. When you turn the ignition key or press the start button, the switch activates the car’s electrical system.

It controls the flow of electricity, allowing current from the battery to flow to the ignition coil. If the ignition switch malfunctions, it can drain power from the battery.

This is possible if the ignition switch fails to disengage fully after you turn off the engine. If this happens, some electrical circuits can remain active, slowly depleting the battery over time.

The Starter Motor

The starter motor is an electric motor that turns over or “cranks” the engine to start. It is powered by the car’s main 12-volt battery. The starter motor needs a big electric current to turn over the engine. To supply this current, the battery has to have sufficient power.

When you turn the ignition key to the ‘START’ position or press the ‘START’ button, the engine computer checks various conditions. If all checks pass, the engine computer sends a signal to the starter motor to start the engine.

But here’s the thing: a faulty starter can significantly drain a battery. This usually happens when the starter motor draws more power than usual due to internal damage or wear. It can also happen if the starter stays engaged due to a sticking solenoid, continuously drawing power and leading to rapid battery depletion.

The Ignition Coil and Spark Plugs

The ignition coil is a vital component of your car’s ignition system. It transforms the battery’s low-voltage power into the thousands of volts needed to create an electric spark in the spark plugs.

This spark is what ignites the fuel in the engine’s cylinders. Faulty ignition coils overheat because they can’t efficiently transmit the energy from the battery to the spark plugs.

And we don’t want that, do we? And that’s not the half of it.

If there is a problem with the spark plugs, they can cause a short circuit that will drain your battery. If your spark plugs aren’t firing correctly, it can cause a strain on your battery.

This is because the battery has to work harder to produce the electrical current needed to ignite the spark plugs. Over time, this can lead to damage or even failure of the battery. It can also adversely affect your starter, your lights, or your electronics.

Countless people visit their mechanics because their car batteries keep dying. Sometimes, the problem is with the ignition system. A mechanic can figure out what’s wrong and fix it. This will rescue your battery and keep your car running smoothly.


Alright, let’s move on to the next possible problem – the heater!


We use the car’s heater to stay warm if it’s cold outside. But did you know that if it works too hard, it might drain your battery? In cold weather, running the heater for too long can use up power. As a result, the battery can drain. Best to fire up the motor now and again to top up the battery’s charge.

Power Windows, Seats, and Air Conditioning

Let’s talk about some common features in our cars that can cause battery drain issues. I will guide you through power windows, seats, and air conditioning systems. I will also explain how they relate to parasitic draw and battery drain.

Power Windows and Seats

We often use power windows and seats in our cars. Did you know that if you have a wiring problem or faulty switch, these features can drain your car battery?

A wiring problem or faulty switch can cause a parasitic draw, which is a continuous drain of power even when the car is off. You can use a multimeter or check for signs of heat or sparks in the wires or switches to detect a parasitic draw. You can fix it by repairing or replacing the damaged wires or switches.

To prevent this, make sure always to turn off your power windows and seats when you’re not using them. It’s also a good idea to check your car’s maintenance schedule and follow it. Regular maintenance can help catch issues early on. It can also save your battery from unnecessary draining.

Air Conditioning System

Now, let’s talk about your car’s air conditioning system. We all love a comfortable drive, but air conditioning can also affect the battery. This is because the air conditioning system uses a compressor that is driven by the engine.

When the air conditioning is on, the compressor puts a heavier load on the engine and requires more fuel. This reduces the car’s fuel efficiency and engine power.

The alternator, which is also driven by the engine, charges the battery and provides power to the car’s electrical systems.

When the engine is under more load, the alternator may not be able to produce enough power to charge the battery and run the electrical systems. This can cause the battery to drain faster and the electrical systems to malfunction.

Adjust the temperature settings as needed to minimize the air conditioning system’s impact on the battery. Don’t use the air conditioning at full power for the entire trip.

Periodic maintenance is also essential here. Regular checks of the A/C system can help ensure its proper functioning and prevent it from straining the engine and battery.

Parasitic Draw

Now, here’s the kicker: parasitic draw can also come from aftermarket accessories or modifications that you have installed in your motor.

So let’s look at how that can happen.

Parasitic Draw from Aftermarket Accessories or Modifications

Aftermarket accessories or modifications can sometimes create a parasitic draw. For instance, my car originally had no audio system, security alarms, or other gadgets. I added them myself. These devices can sometimes consume power even when my car is not in use – this is a parasitic draw and can drain your battery’s life.

Annoying, huh?

Here are some things that can cause a parasitic draw from these modifications:

  • An aftermarket audio system that doesn’t properly shut off when my car is off.
  • A security alarm that triggers by accident, drains battery power.
  • An electrical issue with other installed gadgets, causing them to use power continuously.

To avoid these issues, only install aftermarket accessories yourself if you feel confident in your abilities. If not, make sure a professional to install them. They know how to prevent any unwanted battery drain. Regularly checking your car’s electrical system can also help catch potential problems early.

Battery and Driving Issues

Here’s another twist: your battery is not a simple machine. It’s a sophisticated and vulnerable system that can drain rapidly. One of the main factors is that your battery might simply be too old.

Old or Failing Battery

One of the main reasons a car battery drains is its age. An old or failing battery has a reduced capacity to hold charge. So, even a small drain can cause it to die quicker than a new equivalent. Batteries usually last 3-5 years. It’s good to replace them before they cause problems.

Short Trips or Infrequent Driving

Another factor affecting battery drain is your driving habits. Short trips and infrequent driving lead to a higher rate of battery drains. When you make a lot of short drives, the alternator doesn’t have enough time to recharge the battery fully.

In city driving, you often stop and go. This makes the battery use more energy to start the engine frequently. This puts extra strain on the battery, draining it even quicker.

Some electric or hybrid cars have regenerative braking systems. This technology captures energy from braking and uses it to charge the battery. This feature helps to some extent if you often drive short distances.

To maintain your battery’s health, experts suggest occasionally taking longer drives. This gives the alternator ample time to recharge it fully.

Maintenance and Weather Conditions

Did you know that weather conditions can affect your car battery?

It’s true.

Old car with snow on it

Extreme temperatures can make it tough for your car battery to work well. This is especially true of cold weather. To avoid any issues, we need to perform regular maintenance. We also need to be aware of how weather conditions can impact our car batteries.

During cold weather, batteries slow down and lose their capacity. This is because the chemical reaction inside the battery gets sluggish. According to the RAC, at 32 degrees Fahrenheit, a car battery loses about 35 percent of its strength. And at 0 F, it loses about 60 percent. That’s why it’s harder to start your car in the winter.

Sometimes, extreme heat can also harm our car batteries. The battery fluid can evaporate when it gets too hot, causing internal damage. This harms the lifespan of the battery. AutoZone explains that extreme heat can accelerate the chemical reactions within the battery, leading to faster degradation. So, during the summer months, it’s important to park the car in a shaded area or garage when possible.

I perform regular maintenance checks to keep my battery performing at its best. This includes testing the battery charge using a voltmeter or a battery tester. It also involves cleaning the terminals and making sure the connections are secure. If I’m unsure about something, I don’t hesitate to get professional help.

AccuWeather provides some tips on how to protect your battery from extreme temperatures, such as using a battery warmer or insulator in cold weather or using a solar-powered fan or vent in hot weather.

Other Possible Battery Drains

And finally, here’s a roundup of a few other potential causes of the dreaded drain.

  • The radio, GPS, or other electronic devices that are left on or plugged in when the car is off.
  • The headlights, tail lights, or brake lights that are left on or have a faulty switch.
  • The key fob is kept too close to the car, which prevents the car from going into sleep mode.
  • The corroded or loose battery terminals that prevent the battery from charging properly.

Before You Go…

Now that you know what drains your car battery the most and how to deal with those issues. You might be wondering how to keep your battery in optimal condition. After all, you don’t want your battery to degrade and lose its performance and lifespan. You want your battery to work as well as possible and last as long as possible. The solution is to understand and prevent battery sulfation.

This is the process that gradually reduces your battery’s ability to hold and deliver power. In my next post, I’ll explain battery sulfation, how it occurs, and how you can stop or reverse it. Read “What is Battery Sulfation? Expose the Hidden Threat to Your Battery’s Longevity” now.

Frequently Asked Questions

Here’s the FAQs

What causes a car battery to drain when not in use?

Car batteries can drain when not in use due to a few reasons. Parasitic drain, faulty electrical components or dirty connections can cause this issue. Human errors, like leaving headlights on, also contribute to battery drain.

How can an alternator impact a car battery when off?

A broken alternator can negatively impact a car battery. It may cause the battery to drain by not charging it properly when the engine is running. If the alternator is faulty, it can’t power your vehicle’s electrical system, so the battery has to fill in.

What are common reasons for parasitic battery drain?

Common reasons for parasitic battery drain include:

  • Bad door or trunk lock switches.
  • Malfunctioning alarm or other aftermarket devices.
  • Stuck relays in the electrical system.

These problems drain the battery even when the car is turned off.

Why does a car battery die while parked?

Car batteries die while parked due to several factors, such as:

  • Long periods of inactivity.
  • Cold weather.
  • Connections left on by mistake.

These factors can cause a parked car’s battery to die, especially if it has already reached the end of its life.

What factors lead to a new car battery dying?

A new car battery can die due to:

  • Manufacturing defects.
  • Improper installation or poor connections.
  • An extreme temperature shift.
  • Other electrical issues in the vehicle.

Always make sure to have the battery and vehicle’s electrical system checked. If a new battery fails, get it checked.

How can I identify the source of my car battery drain?

To identify the source of your car battery drain:

  1. Perform a parasitic draw test with a multimeter.
  2. Check if all electrical connections are clean and free from dust or dirt.
  3. Inspect the wiring for any damages.
  4. Look for any devices left on when the car is off.

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Steve Brown


Steve is a gadget enthusiast who's always been intrigued by batteries. The founder and editor of Battery Chargers Info, he's assembled a group of like-minded experts to cover every facet of portable power His aim is to help you learn more about your favorite gadgets and their batteries so you can maximize both their performance and their life. Follow him on Twitter: @batterycharge1

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