Why Does My Car Battery Drain so Fast – Hidden Facts

Imagine this: you came back from work, parked your car in the garage, and tried to start your car the next morning but returned to a dead battery. 

Shocking, right? Well, many people experience the same problem.

There can be multiple reasons that may have caused your battery to drain, such as leaving the car’s headlights on, etc. 

In this article, I have provided several reasons that may cause your battery to drain fast.

So Let’s Begin with the Importance of Battery

Before we move on to the causes of battery drain, let’s talk about how important a battery is for a car. It is essential for every vehicle. 

It converts the chemical energy into electrical energy to power your car’s engine up. In addition, a battery provides electricity to a car’s electrical components to get them going.

Why does Car Battery Drain when not in Use?

Now, onto the main question, why a car battery may drain even if it is not being used?

A few things that may cause battery drain when not in use, include the end of the battery’s life, loss of battery connections, a trunk light staying on or a power seat/window, or any other accessory with a bad switch or parasitic battery drain.

The current reading should be 0.03 amp when the engine is off. 

Apart from these, common causes of parasitic battery drain could be:

  • Warm boot light but no indication of light being on.
  • Car alarm could kill the car battery when not in use.
  • Chemical reactions inside the battery.
  • Faulty Relay, Dome light switch or alternator could be the culprit.

What are the Reasons for Rapid Battery Drain?

Many people complain about their battery going dead in no time, and to be honest, I have faced the same.

When I got the same issue, I consulted a service tech, and he told me that there are four main reasons your battery may drain rapidly.

  • The first reason is that if the connections to the battery are faulty, your engine will become super-hot, consuming a lot of energy and eventually killing your battery.
  • My service tech told me that if any wire in your vehicle is short, it will also lead to a rapid battery.
  • If you use a worn-out battery in your vehicle, there will be voltage fluctuations leading to battery drain.
  • Lastly, if the car’s alternator is faulty, it will drain the battery at a fast pace as well.

Why is the Car Battery Draining Overnight?

An unstable tracker unit can drain your car battery overnight, but in most cases, the battery itself is the culprit due to weak storage capacity.

Why Does My Car Battery Drain When It’s Cold?

We all have been taught in our science lectures during our school years that certain things react to changes in temperature. For example, when the weather is hot, the steel bridge expands, and it contracts when the weather is cold.

Similarly, a car’s battery also reacts to changes in temperature. During hot weather, extreme heat speeds up the chemical reactions taking place in the battery.

On the other hand, during cold weather, the chemical reactions in the battery slow down. Eventually, this diminishes the ability of the car to start itself. Moreover, if you are using an old battery in your car, it will drain rapidly during cold weather. 

Therefore, a trickle charger may come in handy for charging your car because it gains back its lost warmth. If a trickle charger is not your thing, you can purchase it to remain your battery at an optimum temperature during the winters.

Trickle Charger

Now a question may arise in your mind about what a trickle charger is?. The simple answer to this question is an external charging device for a car’s battery. You can read more about Trickle Charger Here.

NOCO GENIUS, 2-Amp Fully-Automatic Smart Charger, The key feature of this charger is that you can use it with either 6-volt or 12-volt lead-acid automotive, marine, and deep-cycle batteries.

A built-in thermal sensor detects any temperature change to prevent overcharging in hot weather and under-charging in cold weather. It is also capable of charging any battery that has a charging as low as 1-volt. Buy Now from Amazon.

Do Electric Car Batteries Drain When Not in Use?

Several people who have or want to get an anelectric car, have this concern. To be honest with you, the batteries of an electric vehicle drain but at a very slow rate compared to non-electric vehicles.

There are two solutions to this problem: plugged the charger daily if not in use or drive it every day. 

Let me give you a piece of advice, drive your electric vehicle daily. It is because recently, my friend, an auto technician, told me that electric vehicles are equipped with 12V batteries, so they will eventually go bad if not used for a long time.

How to Identify Hidden Power Drain (Parasitic Battery Drain)?

Earlier, I mentioned that a parasitic battery drain could be a reason for battery drain when the battery is not in use, or the car is parked. Now the question is what a parasitic battery drain is and how it can be identified?

The answer is a hidden power drain, commonly known as parasitic battery drain, which can be something (e.g., faulty relay, alternator, etc.) that continuously drains your car’s battery even if the engine is off.   

Now, that you know about a hidden power drain, it’s time we discuss how to identify hidden battery drain so that it can be easily cured. The foremost thing you require for identifying a parasitic battery is a multimeter.

All you need is a multimeter and follow the below steps to get the job done:

  1. Fully charge the battery using a battery charger
  2. Check for parasitic drain by putting the multimeter on the amp scale
  3. Take leads, and then loose and remove the negative battery cable and put one lead in that cable and touch the other lead to the negative battery terminal and look at the amp draw
  4. Now check what is causing the significant amp draw by following the steps below:
  • Put plastic clamps on the lead and start checking by pulling the fuses one by one
  • Watch the meter for amps to drop, and if you pull a fuse and see if the amps drop, then you have identified the affected circuit
  • Now, check the fuse box; you need to look at every single fuse until you observe a significant drop in amps
  • Hook the meter back up and continue by pulling fuses
  • There is a fuse box with the passenger seat do check it as well

Product Recommendations

Klein Digital Multimeter: This multimeter is one of the best options in the market given how versatile it is; it works as a voltmeter, ampere meter, circuit tester, and many other functions. It is equipped with a double insulation safety rating. Buy Now from Amazon.

Romanend Professional Plastic Clamps: These heavy-duty plastic claps feature rounded so that you can grip with ease. It features flexible and 45 degrees rotatable clamping pads that can adjust various objects. It also includes 3 additional orange clamping, which can be used as a backup if any pad gets damaged. Buy Now from Amazon.

How to Prevent Car Battery from Draining

As you are aware of the causes of battery drain, it’s time we discuss how to prevent this problem. There are numerous ways in which you can prevent your car’s battery from draining. Some of the prevention measures are as follows:

  1. Spraying protective spray on the terminals of the battery or using petroleum jelly to prevent rust. Something that can come in handy is PriorityStart! 12-Volt-Pro-SP Automatic Battery Protector, it is a highly recommended battery protector. It disconnects any current drain when the engine is switched off. Moreover, it doesn’t let your battery die. Buy Now from Amazon.
  2. Charge the battery using a trickle charger and measure the voltage using a multimeter, so you know the battery’s condition.
  3. Install a battery cut out switch.
  4. Regularly check your battery and keep it maintained.
  5. Keep your battery cool during the summer season
  6. Upgrade the computer programming that controls when and how different systems in your vehicle power down when you turn off the ignition.
  7. Remove the alarm powered fuse to disable the alarm.

There are Three Methods of Battery Maintenance

Under the current COVID-19 environment, some people may not be driving their vehicles for long periods of time. Therefore it is important to ensure the maintenance of your car’s battery. 

Driving the Vehicle/Starting the Engine

This is the simplest and easiest method for the maintenance of a car’s battery. There are two things that you can do here. Either you must drive the vehicle for 30 minutes but with all the accessories off and at a speed of over 30mph, or if you can’t drive the vehicle, you should at least start and run the engine for 30 minutes but keep all the accessories off.

External Battery Charging

Another thing you can do to maintain your car’s battery is to use an external battery charger. The purpose of the external charger is to prevent the charge of your car’s battery from draining.

A charger that every professional service tech recommends is CTEK Fully Automatic 4.3 amp Battery Charger and Maintainer. It provides an eight-step approach to battery care. The best thing about this charger is that it improves the charging in all weathers.

Disconnect the Battery Cable

A very common type of battery drain is a parasitic drain. To eliminate parasitic drain, you should disconnect the negative, black-colored battery cable.


It is a fact that every car battery has to die eventually. But to prolong the life of your car’s battery you must keep it maintained in working condition.