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Car Battery Draining Overnight: 7 Things That Can Drain It


As a car owner, the last thing you want to experience is your car not starting. This is especially frustrating if you are in a rush.

While many car’s electrical components can be the reason your car does not start with the ignition, car battery draining overnight is probably the most common culprit.

A drained car’s battery is something you should not ignore. Your car battery draining overnight can be caused by a charging system problem, loose or corroded battery connections, electrical shorts, a faulty alternator, extreme weather, or a problematic or old battery.

Remember, the battery sends power to the starter motor. From there, the engine starts cranking. If you have a drained battery or a dead battery, it cannot supply enough power necessary for ignition. A poorly maintained battery or a weak battery can also cause other vehicle issues.

Don’t worry. A drained battery does not always call for a replacement. There are different reasons for your car to lose charge overnight, which are easy to fix.

7 Reasons Your Car Battery Drains Overnight 

Common Causes That Can Drain A Car Battery Overnight

The battery warning light typically comes on whenever you have battery related problems. This can be your first indicator that there is an issue you need to resolve with regard to your battery.

Once you see this light come on, open the hood of your vehicle and check the positive and negative terminals to see if they have any corrosion on them.

Another thing you can do is conduct a voltage test with a multimeter. Here is a list of all the other things you can check out for a bigger picture:

#1: Worn-Out Components 

Particularly, shorted devices cause circuitry, including relays, switches, and modules, to stay alive even after turning off your ignition switch. Bad wiring and lack of awareness are to blame for this issue.

Fortunately, resolving this issue is straightforward after figuring it out. You can pull fuses one by one, isolating the root cause of the problem.

#2: Parasitic Drain 

During a parasitic drain, your car battery continues to discharge even after the engine has been shut off. It can also result in battery failure. When the engine is turned off, the car’s battery still supplies power to some components, like anti-theft and clock features.

Parasitic drain takes place when your car battery sends to other components that should not be charged after turning off the engine.

Also, a parasitic drain can be a result of different factors, but the number one cause is leaving cabin lights, glove box lights, or headlights on overnight. Poor or improper installation of new car batteries, bad wiring, and defective fuses can also cause a parasitic drain.

You can check for parasitic drain by disconnecting a battery cable and checking for current flow. Use the highest possible amperage setting if you plan to use a multimeter. Also, you can check for a drain by disconnecting the negative battery cable. Then, you need to complete a circuit between the ground and the negative battery terminal.

#3: Extreme Temperature 

Extremely hot or cold weather can cause your car battery to drain overnight.

Even just for a night, cold weather can already impact your car battery. The chemical reactions within your car battery slow down. If you leave the car battery in the cold for long hours, the chemical reactions will stop completely.

Hot weather can cause car batteries’ chemical evaporation, which results in a quick drain. So, ensure to keep your car in a well-ventilated or well-conditioned room if you live in an area with extreme temperatures.

#4: Defective or Bad Alternator 

An alternator is responsible for recharging the car battery every time it is put in gear. It also produces a constant electrical power flow to the car’s accessories. However, a defective alternator diode causes unusual noises, flickering lights, and other car battery problems.

Once the alternator becomes defective, the car’s battery keeps draining and fails when you start your car. The best thing you can do here is to jump-start your car. This helps your vehicle obtain sufficient power to drive down to a repair shop.

#5: The Car Does Not Turn Off Properly 

Did you forget to turn off your car properly last night? This is a common reason your car loses charge quickly. For example, the car door or the boot is not shut down all the way, or you left the interior or headlights on can cause the car battery to drain.

Many cars require manual effort to shut off the lights if they have been on for long hours or send a warning beep, while some cars can automatically do the job. If you do not fully turn off your car regularly, the lifespan of your car battery shortens because of a constant drain.

So, before leaving the car, check the lights and doors to see everything is locked up and switched off properly.

#6: Faulty Sensors 

If your car features an automatic light mode, it has sensors located in the rearview mirror, in the middle of the dash panel, or behind the windscreen. These sensors promote the proper functioning of the automatic light mode. They determine whether light conditions outside your car have changed and prompt night mode or lights to be activated accordingly.

However, once these sensors fail, your car’s automatic light feature does not work as well. This causes various lighting assemblies to remain on even if they are not supposed to. If the car battery runs on low charge before this issue, it will drain overnight.

#7: Corroded Battery Terminals or Loose Battery Cables 

The car battery’s positive and negative battery terminals are where cables are attached. When doing car maintenance work, you should always disconnect them for safety reasons. And you must ensure proper reconnection.

Car batteries usually come with plus and minus symbols for terminal identifications. The convention is often a black cable for negative and a red cable for positive, but it is not always the case. Make sure to disconnect the negative cable first.

Your car’s battery can discharge if the cables become loose. A hot ground wire cable, issues starting the car, and flickering headlights are some of the signs of loose cables.

You can fix this issue by tightening the cables and then re-installing them correctly. Always remember the safety considerations when working on electrical systems to prevent damage or shocks. Please note that qualified mechanics should only handle electric, hybrid, or recent vehicle models.

Another reason for your car battery drain or poor performance is corrosion around the battery terminals. You can disconnect the vehicle battery to clean the terminals using a diluted baking soda mixture with a brush. Then, apply petroleum jelly to them and reattach the cables. Again, take safety conditions while doing them.

How to Prevent Car Batteries from Draining 

Now, it’s time to talk about several ways to prevent your car battery from draining. Consider the following tips to keep your car battery healthy:

#1: Keep Driving 

To ensure the alternator does its job while preventing the car battery from getting discharged, drive your car after every few days. Driving your car regularly also helps the engine lubricate and prevents flat spots by reducing strain on the tires’ bottom part.

#2: Shut the Car Properly 

Do not just lock your car; ensure to switch it off properly. Check if the headlights and interior lights are off and if accessories like USB ports and charger sockets are switched off. If you turn the GPS or car radio on once the engine is off can drain the car battery. So, avoid doing this thing.

#3: Avoid Short Trips 

Do you always use your car on short trips? Please note that frequent short trips can strain the car battery. Instead, use your vehicle for an extended period once on the road. Also, you can invest in an external battery charger to keep the ideal voltage if you use your car for long journeys or cannot use it often.

#4: Be Cautious of Warning Signs 

Here are some signs that your car battery drains quicker than usual:

  • Car’s dashboard illuminates once the battery is down.
  • Car starts making the usual sounds or noises.
  • There is a clicking sound when you turn the ignition key on.
  • Car accessories do not function effectively.
  • The dashboard lights are dimmer.
  • The battery connections are corroded or loose.

Once you notice any of these signs, ensure to inspect your car as soon as possible or bring it to the professionals to prevent further battery deterioration.

#5: Check the Car Battery Regularly 

You can lift the bonnet to see signs of wear and tear. And while inspecting the battery, make sure the following:

  • The voltmeter is around 12.7V or above.
  • Battery terminals are not corroded.
  • The top of the battery is free from grime and dust.
  • The battery is tightly fastened.

#6: Invest in a Trickle Charger 

This charger utilizes the battery voltage regulator to charge the car battery with a similar amount and speed. This prevents your car battery from becoming flat if your vehicle has been parked for a long time or from overcharging. The charger is especially helpful if you only use your car during special occasions or park it for long periods.

#7: Keep the Car in the Garage 

Keeping your car in the garage helps protect its battery from extremely hot or cold conditions. Alternatively, you can park it in the shade. Also, you can invest in a battery blanket to avoid car fluids during winter days.

What to Do If Your Car Battery Keeps Dying?

Have an alternator diode test done as soon as possible if your car battery keeps dying. This will let you know if the battery is being recharged by the alternator or not. You might need to have your alternator tested if it isn’t.

Your car’s electrical system may be operating inefficiently and quickly depleting the battery due to a defective alternator. If so, replacing it is probably the best course of action. Make sure the alternator belt is free of cracks and other signs of wear, as this can cause the alternator to be inefficient.

Modern vehicles have numerous power-hungry features that may drain the battery if they are left on when the engine is off. If no signs of a battery discharge are found, you may need to replace the battery itself. Since your alternator recharges your battery, it is critical to identify and address any underlying problems as soon as possible.

Should You Check For Other Battery Power Drainers?

The amount of draw being put on your battery can be measured using a digital multimeter. A multimeter is a device that assists in determining the electrical draw and current of a component. Connecting the multimeter is something that should be done with the ignition off.

To perform a parasitic draw test, start by setting the multimeter to measure current and attaching it to the negative battery post of your battery. Next, start pulling fuses out one at a time while keeping an eye out for variations in the multimeter’s reading. If you notice a high voltage drop, then you’ve found the problem and can take steps to make the proper repairs.

Check any other electrical component pulling power from the battery when the vehicle is not turned on, like the fuel pump, amplifier, dome light, alarm system, trunk lights, or any other part that may drain the battery overnight.


Most causes for car battery drain overnight mentioned above can be addressed at home. However, make sure to use the appropriate tools and skills. If you are not confident about fixing the issue, do not hesitate to contact professionals.

Of course, prevention is always the best course of action. Make sure always perform a visual inspection, battery drain test, or battery terminal test, and perform proper maintenance. These are most of the things you can do when your battery dies.

Your battery’s lifespan will depend on how well you care for it. That is why it is important to perform regular maintenance checks on your battery and replace it with a new car battery when necessary.

Last Updated on: January 27, 2023

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