Car battery drain overnight: 5 Possible causes and How to fix it

Updated Oct 27, 2021 | Same topic: Handy Maintenance Tips

Avoid these to prevent draining your car battery.

Starting your day with a car that won’t start can be frustrating especially if you are in a rush going to work or school. There are many car components that we can point out to determine the reason why your car won’t start when you turn the ignition key to the ON switch. Perhaps the most common reason for the unfortunate occurrence is due to a car battery draining overnight

EASILY Identify Vehicle Battery Draining Problems(Parasitic)

A car battery is responsible for sending power to the starter motor to start cranking the engine. If your car battery is drained, then it won’t supply the sufficient power needed for ignition.

However, a drained battery does not mean that it’s time for a replacement. There are various causes for a car battery loses charge overnight which can be fixed with few simple steps.

What can drain a car battery overnight: 5 possible causes 

Cause #1: Left components open

One of the most common causes of a drained car battery is human error. We sometimes forget to turn off a car component as we leave our vehicle since we are already tired from work. There are also episodes when we don’t notice that a car light is left turned on especially in broad daylight where it is almost impossible to notice them.

Leaving a car component open overnight while the engine is turned off will cause your car battery loses charge overnight. However, newer production cars tend to come with an alert system that tells you that you have left a component open before leaving your vehicle. 

A classic car's headlight

Be sure to turn off all lights before leaving your car.

Cause #2: Parasitic drain

Parasitic drain is another common cause of why a car battery died overnight. What it does is continues to discharge the battery even after shutting the engine off.

Your car battery is still powering some components once the engine is turned off such as the clock and anti-theft features. Parasitic drain occurs when it sends to other components that shouldn’t be charged after the engine is turned off.

This can be a result of various factors including the number one cause which is leaving headlights, glove box lights, or cabin lights on overnight. Parasitic drain can also be caused by defective fuses, bad wiring, and poor installation of a new car battery.

>>> Related: How to install a car battery safely

Cause #3: Extreme temperature

Cold weather can affect your car battery even you leave it just for a night. When a car battery is left in the cold for hours, the chemical reactions within the battery will be slowed down. Leaving the car battery in the cold for a longer time will cause the chemical reactions to stop completely.

Hot weather can also affect your car battery. With a very high temperature, it will evaporate your car battery’s chemical which will easily drain it. As such, you should keep your car in a well-conditioned room if you are in a place where extreme temperatures are present.

Checking a car battery's voltage using a multimeter

The voltage reading of a car battery should be around 12.6 to 12.8 volts

Cause #4: Faulty alternator

Alternators are installed in automobiles to power the electrical system once the engine is turned on. It is driven by the crankshaft through the serpentine belt. Another function of an alternator is that it charges the battery after ignition. If your car has a faulty alternator, then it could drain your battery since it is not charging properly.

Driving short distances is also a cause for draining your battery. An alternator needs some time to charge your car battery after ignition. As such, short trips are bad for your car battery since they will not fully recover. You should leave your car running for at least 10 minutes after a short trip to avoid car battery dies overnight,

Cause #5: Age

If your car battery is due for replacement, then it always will be drained overnight even after a series of charging it. Car batteries are like cellphone batteries. Over time, your cellphone battery will lose power faster as compared to the time you first bought it which means that it is due for replacement.

On average, you should replace your car battery every three to four years. Some may even reach five to six years, depending on the usage and how many accessories you have installed in your car. Driving your car way past the expected shelf life of your car battery will only result in a constantly drained-out battery.

Car battery in an engine bay

If your car battery is due for replacement, do so to avoid difficulties in starting the engine

How to fix a car battery dies overnight

If your car won’t start, then it could mean that your car battery is drained. You can still jump start it using sources of electricity such as a portable jump starter or a good battery from another vehicle. 

To use a portable jump starter, simply connect the positive clamp of the portable jump starter to the positive terminal of the drained battery first before connecting the negative terminal. Turn on the portable jump starter and start your car after one to two minutes.

Jump starting a car with jumper cables

Jump starting is one of the things you need to know when owning a car

>>> Related: Car battery charger price Philippines: Top 5 products in 2021

To jump-start using another car’s battery, you need to have jumper cables. The first thing you need to do is to turn off the engine of the car with a good battery. After that, connect the positive clamp to the positive terminal of the drained battery then to the good battery.

The next step is to connect the negative clamp to the negative terminal of the good battery and connect the other end to a grounded and unpainted metal in your car with a dead battery.

Start the car with a good battery to charge the drained battery. After at least a minute, you can now start the car with a drained battery and it should work.

A car battery in an engine bay

Keep your car battery in good condition to avoid unwanted replacement costs

Now, if your car battery is already running for around four years, then it could mean that it needs to be replaced. On average, a new car battery in the Philippines will cost you around Php 5,000, depending on your chosen battery. But, if you recently replaced your car battery, then it could mean that you left a light on overnight causing it to drain.

FAQs about car batteries

1. What does a car battery do?

A car battery is mainly used to power the starter motor during ignition.

2. What should the voltage of my car battery be?

You should get a voltage reading of around 12.6 to 12.8 volts to make sure that it is still in good condition.

3. How much is a car battery in the Philippines?

The price of a new car battery in the Philippines ranges from Php 3,000 to Php 7,000.

4. What does an alternator do?

An alternator provides electrical power to a car once the engine is turned on.

5. How long do car batteries last?

On average, car batteries last for around four to six years.

That is all you need to know regarding car battery draining overnight. Here at, we value your interest in the automotive industry. Visit our website to find out more.

Rex Sanchez

Rex Sanchez


Rex Sanchez grew up in Saudi Arabia where he saw and got into the automotive scene. He started his career for an aviation company in the said region, writing about turbines and rotors which are later distributed for educational purposes. And now, he joined as a staff writer. Currently, he is the youngest on the team and is more than ready to grow in the field.


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