What Can Drain a Car Battery When it’s off?

Your car battery was full and functional the last time you parked your car. But now, the car won’t start since its battery is dead. What could have drained the battery overnight?

There are many possibilities that can drain and leave your car battery dead, even when the car is off. Today, this post explores six possible solutions. But first, what is the significant of a car battery?

What is The Work of a Car Battery?

Without a car battery, your car won’t start?  To start your car, you must first insert the key in the ignition to switch it on. The car battery receives the signal in chemical reaction form, then converts it to the electrical power needed to start the car.

Afterwards, electrical energy is sent to the starter to start the engine. On top of that, it also provides power to other electronic components of the car so they can remain functioning.

6 Possible Causes of Battery Drain

1. Parasitic Drain

You remember turning off your car, not even a single door was left open, but the car battery was still dead by morning. That’s quite a frustrating moment, but it happens. Electronic devices such as the radio, amplifier, power mirrors, glove box lights, and more could be draining the battery.

This is called a parasitic drain, but it shouldn’t go beyond 75 milliamps. When it goes beyond the normal range becomes a problem that can significantly affect the performance and lifespan of your car battery.

2. Temperature Extremes

The extreme weather outside can drain your car battery even when the car is turned off. Any temperature below 10 or above 100 degrees Fahrenheit doesn’t sit well with the car battery as these are either extremely hot or cold conditions.

You shouldn’t turn off your car for long in such weather conditions since lead sulfate crystals will accumulate, which will drain whatever percentage is left on your battery. Charging it also becomes a problem since it will take too long before it can get fully charged.

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3. Personal Causes

Human beings are prone to errors, which is also one of the leading causes of car battery drain. You may have forgotten to do routine checks before leaving your car.

For instance, you didn’t switch off the headlights, or close the trunk. When these happen, the battery will still be sending power to these components until it runs out of power. You’ll receive an alert if you leave any lights on in most cases, but this doesn’t always cover all the components.

4. Your Car Battery Is Old

A car battery can last between 4-5years, but this can change depending on several factors, like the weather. It means that any car battery beyond five years old is probably worn out, so it won’t hold a full charge like it used to before.

Over time, a car battery’s ability deteriorates until it can’t provide enough power needed to start your car. An old battery will discharge by itself when you park your car for a long time.

5. The Battery Cables Are Either Loose or Corroded

The two battery cables usually connect to the positive and negative terminals of the battery. When these cables are loose, it may become difficult for your car to start due to often shaking, even with a fully charged battery. For this reason, ensure that the battery cables are well-installed and tightened to avoid shaking.

Cable corrosion is also another problem you have to deal with to ensure your car battery remains effective. Look for the signs of corrosion around the battery terminals, such as blue or dirt-like substances. You can use a dry cloth or toothbrush to wipe them off.

6. Having Many Short Drives

Having too many short drives can shorten the lifespan of the car battery and make it unable to hold a charge after you’ve parked. Your car uses a lot of power from the battery when starting, and so you need to drive it long enough for the alternator to recharge the used power.

Remember, the alternator can only recharge a car battery when you’re driving. The short drives can only mean that you always shut your car before the alternator can finish its work.

How to Keep Car Battery from Dying When Not in Use

Now that you know the possible causes of your car battery draining, you probably need a lasting solution. Thankfully, you can do these activities to manage these possibilities.

  • Ensure that all the internal lights and all the electronic components are off. Again do correct latching of the doors, trunk, and glove box to prevent parasitic drain.
  • Make sure that the battery is always clean
  • Avoid loose battery cables and corrosion by properly tightening them and cleaning the areas around terminals
  • Buy a battery maintainer to keep your car battery charged and also avoid overcharging.
  • Consider replacing your car battery after five years
  • Carry out a regular maintenance of the battery

How to Test for Battery Drain

As you can see, a parasitic drain is one of the causes of battery drain when your car is off. But how can you confirm this as the main cause? Thankfully, a digital multimeter could be of great help in this case. Follow these steps.

Connecting a digital multimeter to the negative terminal of your car battery will help you find the culprit. But first, ensure that the battery is fully charged before you can put it to this test. Once connected, remove the fuses one after the other as you look out for the changes on the multimeter reading.

If you remove one and don’t notice any changes, return it and remove the next until a drop in the reading happens. That right there is the culprit.

When to Get a New Battery

The average lifespan of a car battery is between 4 to 5 years; it’s only fitting that you replace yours after this period. However, this might not be the case, these signs will tell you that you need a new battery, even before this period elapses.

  • The car struggles to start
  • You get dim headlights
  • There’s a foul odor every time you’re driving
  • You’ve jump started it severally now
  • Your car won’t start even with the engine cranking.
  • You may consider buying a car battery from these recommended brands for a change, Odyssey, EverStart, DieHard, and Braille, and Deka.

Frequently Asked Questions- FAQs

What causes my new battery to drain?

Possibilities include internal lights left running, a faulty charging system, extreme weather, human error, or a worn-out alternator.

How long should my car battery hold charge?

A car battery is in good condition; it should take at least two weeks without the need to start the car.

How much car battery drains overnight?

A car battery should only lose up to a tenth of a volt overnight. Anything beyond that is not normal.

Will my car battery drain if disconnected?

No.  You may decide to disconnect one or even both.


Hopefully this article has given you some insights into what can drain your car battery when it’s off, and how to make sure that it doesn’t happen to you. As you may have already noticed, there are a lot of devices that can do this seemingly simple task, and there are a lot more out there too. So take these tips and apply them for yourself to make sure that your battery is being taken care of properly, and that it lasts as long as possible.

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