Car Battery Draining Overnight [7 Causes]

If you are not careful in shutting off electrical gadgets in your car, you may lack battery power the following day when you start your vehicle. However, that’s not the only cause. In this article, I’ll discuss your car battery draining overnight – the leading causes.

Many things can drain the juices of your battery overnight, including:

  1. An electrical device left running overnight
  2. Malfunctioning alternator
  3. Parasitic drain in the battery
  4. Corroded or loose battery connections
  5. Old battery
  6. Extreme temperatures
  7. Frequently going on short drives

You can find out what is draining your car battery using a digital multimeter. Connect your negative (black) battery terminal to the multimeter. Then disconnect the electrical fuses of your car at the fuse box one at a time. Watch for any change in the reading of the multimeter. If the reading drops when you remove a fuse, that is the culprit.

Read on to learn more about why the power of your battery can drain overnight and the leading causes of why this can happen.

Car Battery Draining Overnight

car battery draining overnight

Seven things can drain your battery overnight:

  1. An electrical device left running overnight
  2. Malfunctioning alternator
  3. A particular “parasite” is draining the juices of your battery
  4. The connections of your battery are either corroded or loose
  5. Old battery
  6. The battery is operating under extreme temperature
  7. You are mostly driving on short trips

It’s easy to find out why your car battery keeps draining overnight. Get a multimeter and connect it to the negative terminal of your car. Then disconnect the electrical fuses in your car one by one. Watch for the change in the reading of the multimeter.

You have found the culprit if there is a drop in the multimeter reading. Now you can take the necessary steps to fix the problem. If you don’t know how to fix the problem, you can call a competent mechanic and ask for their help.

A blown fuse can cause a parasitic drain on your battery. This can happen if your car’s electrical system is not working well. There are issues such as bad fuses, faulty wiring, and interior lights that can’t shut off that can lead to the overnight draining of your battery.

There are cases wherein the battery drain is so severe that your battery will be depleted of its juices that you can’t start your car. You must ensure that all electrical components are turned off once you shut off your car engine.

What Is the Most Common Cause of Car Battery Drain Overnight?

It’s annoying to start your car in the morning, and it does not respond. You won’t be able to go on your scheduled trip for that day.

You can avoid this from happening if you are aware of the reasons why this can occur. Seven things can make this happen, and they are all avoidable. What are these seven things?

1. An Electrical Device Left Running Overnight

Forgetting to turn off an electrical component of the car is one of the most common causes why the car battery is dead after sitting for a few days. This is attributable to human error. Thankfully, most modern cars use an alert system that will warn you if you forget to turn something off.

This can also happen in broad daylight. Since you won’t readily notice that an electrical light is still on because of the sunlight, it is easy to leave it on when you have already shut off the engine. The key is to be aware of putting off all electrical components before shutting off the engine.

2. Defective Alternator

car battery draining overnight causes

Once you turn on the engine, the alternator is installed on your car to sustain the battery’s electrical energy to power all its electrical components. It has a serpentine belt that is driven by the crankshaft. The alternator is also responsible for charging your battery while you are driving.

If your alternator is not functioning correctly, it won’t be able to do its functions. If you don’t fix a malfunctioning alternator, there’ll come a time when you turn off the engine the evening before, and you will not be able to start your engine the morning after.

3. Forgot to Turn Off Your Headlights

This is directly related to not turning off your electrical components. However, forgetting to turn off your headlights has a much more severe effect on the battery since they consume a high volume of energy.

So, if you leave them on once you turn the engine off, the battery’s reserve power will be quickly depleted. Your battery will be depleted, not even overnight. It will only take a few hours to consume all that power.

Again, what would cause a car battery to drain overnight? A car battery will drain overnight when you left the amplifier, glovebox light, or any electrical device on. This device’s power supply solely comes from the battery since the alternator isn’t on.

4. Parasitic Draining Off the Battery

Electrical gadgets in your car consume battery power even if you have turned the engine off and ensured that all the usual electrical devices are turned off as well. These are electrical gadgets like the alarm system and the clock.

They are not the usual parasite that can drain off power from your battery. The culprits can be door lights, interior lights, and even bad relays.

This drain can also occur when power is consumed by other electrical components that shouldn’t be charged after you turn off the engine. It could also be because of bad wiring, poor battery installation, and defective fuses.

When you shut off the engine, the alternator is no longer doing its work in recharging the battery. So, if parasitic drains go on overnight, they can quickly drain the battery power considerably.

To prevent this from happening, ensure that you have fully closed all the doors, the glove box, and the trunk so their interior lights won’t consume any power.

5. Loose or Corroded Battery Connections

The connections in your battery can get loose or corroded over time because of their exposure to the stress and strain of the elements. You will have difficulty starting your engine when this happens because it cannot provide your car’s initial cranking energy.

Your engine could even stall while you are driving if your battery connections are in this defective condition. You can prevent this by regularly inspecting and cleaning your battery connections and terminals.

6. Old Battery

Your battery has only a designated life span. You can’t use it forever. So, if it drains out overnight, perhaps it is already past its dutiful life. In the best scenario, a car battery can only last up to five years. On average, it is only from two to three years. More than that is already a bonus for you.

But a battery’s lifespan also depends on how you use your car. If you always drive in extreme conditions and temperatures, that normal life can be considerably shortened. If jump-starting your battery isn’t enough to wake it up, maybe it’s time for you to replace it.

7. Weather Is Too Cold or Too Hot

If the weather outside is too cold or too hot, it will affect the operation of your battery. This is more pronounced in older batteries. Newer batteries are more resistant to extreme temperatures.

Extreme cold will produce chemical reactions in the battery that will cause it not to deliver power when needed. A very hot temperature will also cause the battery fluid to evaporate more quickly. So, if possible, park your car where the temperature is regulated.

8. Short Trips

Starting your engine requires a huge amount of power from the battery. So, if most of your daily trips are for short drives only, so much power is required to be delivered by your battery. The alternator needs sufficient time to recharge your battery.

But if you only frequent short trips, the alternator won’t have sufficient time to recharge your battery. So, when you shut off your engine, you may find that you can’t start it the following day because your battery lacks the required cranking power.

How Can A Defective Alternator Cause Battery Drain?

If your alternator is not functioning correctly, it won’t be able to do what it is supposed to. An alternator is designed to sustain battery power by recharging the battery while you are driving your car.

However, if your alternator is not working well, it won’t be able to recharge the battery. So your battery will keep on shouldering the power requirements of your car while you are driving it.

If your alternator is still functioning but not at its optimum level, you can still drive your car while running.

However, since the battery is no longer adequately charged, once you park your car in your garage and shut its engine off, likely, you can’t start it the following day because its reserve power is completely drained out.

How Do I Stop My Battery from Draining Overnight?

car battery keeps draining overnight

By paying attention to the condition of your battery, you will be able to ensure that it will provide you with all the power you need to start your engine every time you turn on the key. How do you do this?

Here are some tips:

  1. Inspect your battery regularly, if possible every day, before starting your engine.
  2. Look for signs of corrosion on the terminals and the connections.
  3. Ensure that the positive and negative wires of your car’s electrical primary wiring system are correctly connected to their respective terminals in the battery. The positive (red wire) should be connected to the positive (red) battery terminal, and the negative (black wire) should be connected to the negative (black) battery terminal.
  4. Always check every light and gadget is turned off before leaving your car in the parking lot.
  5. If your battery is more than three years old, consider investing in a new one. This will ensure that you won’t be caught with a dead battery anytime you need to drive your car.

In Closing

A lot of things can cause the draining of your car battery. Here are the usual culprits:

  1. An electrical device left running overnight
  2. A malfunctioning alternator is not functioning well
  3. A parasitic drain is leeching off your battery’s juices
  4. Loose or corroded battery connections
  5. Old battery
  6. Extreme temperatures
  7. You are frequently going on short trips

Don’t be caught with a dead battery in the morning. By noting these causes, you can avoid this stressful experience.