UniEnergy Technologies Battery » 6 Common Reasons That Drain Car Battery

6 Common Reasons That Drain Car Battery

We don’t think about our car battery draining until it becomes a problem. Batteries are usually dependable, and they work steadily until they age out around 3 years.

Unfortunately, our batteries can drain prematurely due to misuse or electrical problems. This usually happens overnight, but some issues pop up while you’re driving and cause further issues.

Keep reading to learn the most common causes of a drained battery, how age relates to battery drainage, and how you can fix the problem. We also explain how to maintain your car battery to prevent charge issues in the future.

Common Car Battery Drains

The most common reasons your car battery loses charge or dies completely include:

  • Leaving certain components or accessories on
  • Issues in your charging system
  • Parasitic drain
  • Extreme temperatures
  • Poor battery connections
  • Short drive times

These issues are usually easy to determine, and in this section, we’ll explain why it happens and what you can do to fix the issue.

1. Components Accidentally Left On

The most common reason for a dead battery (without previous warning) is leaving on certain components or accessories, such as your headlights, interior lights, or other electrical devices.

This usually happens if you park your car and forget to turn off your headlights manually, or if you run back out to grab something and leave your interior lights on when you’re done.

It may seem like a slight draw, but it’s enough to drain your car battery of the power it needs to start the vehicle and run other components.

If this is the issue, your car should be fine after jump starting.

To fix this, be more diligent about turning off electronics when you exit the vehicle. Make sure the vehicle is on if you’re sitting in it for an extended period and implement auto-shutoff features when available.

2. Charging System Issues

Your vehicle uses several components to make sure your car battery keeps up with its tasks. If you have a drained battery, look to these parts:

  • Alternator: The alternator uses an electromagnet to generate the electricity needed to recharge the battery. Older vehicles may use a dynamo.
  • Voltage regulator: The voltage regulator ensures the battery receives the proper voltage for charging. If it fails, the voltage may not sufficiently charge the battery.
  • Serpentine belt: A faulty serpentine belt may fail to spin the alternator, leading to charging issues.
  • Tensioner pulley: A worn-out tensioner pulley causes issues in belt tension (usually a loose belt) that fails to power the alternator.

You can test some parts, such as your alternator or voltage regulator, using a multimeter or a voltmeter to determine whether they are working properly. Belt or pulley issues are noted by distinct squealing noises or obvious wear on either part.

A vehicle with charging issues usually dies the moment you disconnect the assisting vehicle after jumping your car. Replace any suspect parts and then check the car again. If you’ve replaced any electrical parts recently, check for poor installation.

3. Parasitic Drain

Parasitic drain refers to anything drawing power in your car when it is not supposed to, usually after you turn your car off. Some parts in your electrical system, like your clock or radio, run all the time to maintain data or preferences, but this isn’t enough to kill your battery.

Most batteries can handle a parasitic draw of 50 to 85 milliamps (lower for older vehicles), but anything beyond this will likely kill your battery while the vehicle is off.

A multimeter is the most effective tool in diagnosing parasitic draw, and it can help you narrow down where your parasite is.

4. Extreme Temperatures

Extreme Temperatures

Extreme temperatures, particularly higher temps, can lead a car battery to premature failure. This is why drivers in warmer states tend to replace their battery on a 3-year schedule, while northern drivers get closer to the 5-year mark.

This varies depending on battery quality, but you can limit the effects of head damage by parking in the shade whenever possible. Battery cleaning and maintenance are even more important with higher temperatures that catalyze any small issue.

5. Poor Battery Connections

Your engine bay is not the cleanest part of your car, and you should expect some dirt or debris to build up on your components over time. Unlike other parts of your car, your battery has exposed parts that may be affected without proper cleaning.

Dirt usually isn’t enough to interfere with charging completely, but issues such as corrosion, loose battery cables, or damaged cables will finish the job.

Make sure you inspect your battery and its connections regularly. Clean off any dirt or debris. Some battery corrosion is normal, especially with an old battery, but it shouldn’t get out of hand. Clean it off whenever you see it to prevent compounding issues.

(Wear protective clothing when handling corrosion on your battery terminals, including gloves and goggles. Remember to disconnect the battery and neutralize the corrosion before you move in with a gentle wire brush.)

6. Short Drive Times

In some cars, taking frequent brief trips drains your battery over time. The trip may not be enough to recharge your battery completely, especially if you’re the type to sit in your vehicle after turning it off and burn through some of that charge.

Make sure you throw in a few trips that last longer than 20 minutes, or let your vehicle run idle for a few minutes to complete the charge. Alternatively, you can use a 12-volt charger to maintain a proper charge.

How Age Affects Battery Drainage

Unfortunately, car batteries don’t last forever. They usually wear down within 3 to 5 years of use, although the exact time varies depending on:

  • The quality of the battery
  • Maintenance
  • Environmental factors (primarily temperature)
  • Improper installation or faulty components

The better conditions your battery is kept in, the longer it should last. Poor conditions cause the internal components of the battery to wear out faster, decreasing capacity and limiting charge effectiveness.

Signs of a Weak Battery

Signs of a Weak Battery

Signs of a weak battery, whether from age or other conditions, include:

  • A battery light or warning on your dashboard
  • Dim headlights or other components
  • Electrical issues (such as some parts not working)
  • A slow starting engine
  • Check engine light

A battery can also go out with no warning, so it’s recommended to change your battery within that 3 to 5 year window.

Further Drained Battery Diagnosis

Make sure you diagnose your drained battery as soon as possible. Sometimes, it’s obvious that you left the lights on, but you should always double check battery condition just in case.

Auto parts stores like AutoZone or battery supply stores will usually test your battery for free. Their tests are more comprehensive than an at-home check with a multimeter, and they load-test your battery to determine its overall health.

You can also test other electrical components, such as your alternator or starter, to determine what needs replacement.

Test for a Parasitic Drain

Testing for parasitic drain is something you can do easily from home with a multimeter.

To do this, make sure your vehicle is turned off and then connect the multimeter to the battery. If it reads a draw over 50 milliamps, keep the multimeter connected to the battery and start pulling fuses.

If you pull a fuse and the reading drops, figure out what’s connected to the fuse. In some cases, there are a few components to run through before you find your culprit (i.e. the power antenna and radio in your audio system).

You can keep the fuse pulled if the component is non-essential to prevent the draw, but it’s important to fix the issue as soon as possible. Electrical issues have a tendency to cause problems down the line.

Preventing Car Battery Drain

Preventing Car Battery Drain

In most cases, proper maintenance is your most effective tool in preventing car battery drain. Apart from replacing faulty parts and following proper running procedures, make sure you:

  • Clean your battery regularly. This includes dusting off dirt and debris and clearing off any corrosion. Check on your battery often, including its casing and cables, and clean as needed, but plan to deep clean the terminals at least once a year.
  • Verify proper installation. While it’s uncommon, your car battery may loosen over time. The excess vibrations from improper installation will damage internal components and age the battery prematurely.
  • Protect your battery from the elements. Park in a garage or under cover when possible. If you live in a colder climate, you can use a battery blanket to protect the liquid solution from the cold.

Without these measures, you’re practically learning how to drain your car battery. Just like any other investment, you need to take the time to maintain and preserve battery health.


Car battery technology is moving forward at full speed, but the issues we face remain the same. A drained car battery is usually caused by human error, but some situations require further diagnostics.

Remember to:

  • Check and clean your battery regularly.
  • Allow it to charge completely
  • Protect your battery from extreme temperatures
  • Replace your battery every 3 to 5 years

Do you need help with your drained car battery? Comment any questions you may have!

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