What can drain a car battery when the car is off? If this question is also yours and you need an answer, then continue to read and take action to stop your car battery from draining when it’s off.
Even a brand new car battery can drain when the car is off completely. Over the years, I have experienced many car battery draining issues when the car is off.
By running some tests on your car, you can stop a car battery from draining when the car is off.
Detecting dead car battery signs in the car is a little bit confusing, so knowing what can possibly drain a car battery helps you to keep the car battery healthy.
But, letting your car battery drain for a long period of time makes the car battery obsolete, and eventually, the car battery needs to be replaced.
What Can Drain A Car Battery When The Car Is Off
Parasitic draw on the battery, left lights on, excessive corrosion, and car accessories drain a car battery when the car is off. To stop your car battery from draining when the car is off, you need to run some tests on the car.
Here is a list of things that can drain a car battery when the car is off:
- Car’s Electric Problems
- Parasitic Draw On The Battery
- Car Accessories
- Defective Alternator
- Excessive Corrosion On The Battery
- Car’s Headlights On
- Car Battery Too Old
- Charging System Failure
1. Car’s Electric Problems
Whether you call it vehicle electrical problems or electric glitches, both are the same thing.
Several electric problems in the car can drain a car battery when the car is off. A car’s electrical system depends on the battery to supply power for the car to operate.
Car electric problems occur for bad battery cables, failed spark plugs, blown electrical fuses and more reasons.
When a car’s electric glitches exist, it starts to drain the car battery even when the car is off completely.
Regular car electrical system check-up with a professional is the best way to avoid any electric problem in your car.
Try to address electrical problems in your car as fast as possible because eclectic problems also cause costly battery replacement.
Related Article: How To Move A Car With A Dead Battery
2. Parasitic Draw On The Battery
When a car’s electrical system consistently consumes energy from the battery, even when the car is off, that is called a parasitic draw on the battery.
As a vehicle owner, you might know a little bit about the parasitic draw on the battery. The parasitic draw can keep a car battery dying in any situation.
Every electrical component in a vehicle draws a certain amount of battery charge, which is totally normal. But, parasitic draws keep draining the battery energy when the car is off.
Between 20 milliamps to 50 milliamps is completely fine, but if the parasitic draw goes up to 75 milliamps, it can make a car battery dead.
For several reasons, the parasitic draw can occur on the battery. So, it’s necessary to run a parasitic draw test when it’s needed the most.
If you experience a drain on your car battery when your car is off, you should definitely run the parasitic draw test by an automobile mechanic.
See Also: What To Do When Car Battery Dies
3. Car Accessories
No matter what types and how long you use car accessories, it drains the battery energy.
Car owners use accessories on cars for different reasons and also for some necessity.
But, the issue with car accessories is that it consistently draws charge from the battery.
Often I see unnecessary car accessories drain a car battery when the car is off. When your car is totally shut off, it reserves the charge to crank it, but that charge can drain by car accessories.
Therefore, you might often experience your car cranks but do not start. By eliminating unnecessary car accessories, you can keep your car battery from dying quickly and efficiently.
Use only necessary car accessories, and if you do not need any accessories, that is even best for your car battery health.
There are numerous unnecessary car accessories available to buy online so ensure you’re getting one that your car actually needs.
4. Defective Alternator
An alternator is the key component of a car battery; that’s why vehicle owners must be more aware of alternator maintenance.
Alternator’s job is to convert chemical energy to electrical energy in a vehicle. So, when you have a defective alternator, it won’t be able to charge your car battery.
A bad alternator cannot recharge the battery, and that is also what can drain a car battery when the car is off.
You need to inspect any loose connection between the battery and alternator. The alternator wire connection must be tight enough.
In some cases, I find corroded alternator diodes drain a car battery when the car is off.
Therefore, ensure your car’s alternator connections are well organized, and there is no corrosion on alternator diodes.
5. Excessive Corrosion On The Battery
As we know, corrosion on the battery can cause several battery issues that are not good for the entire car’s electrical system.
Decreasing the car battery power is the most common sign you will experience when your car battery is corroded.
Excessive corrosion on the battery also creates less energy flow through the battery terminal.
Corrosion would drain a car battery when the car is off and can damage the car battery life, which also affects battery lifespan.
Keeping the battery clean is always recommended for vehicle owners, whether it’s a new or used car battery.
There are various ways to clean corrosion from the car battery terminal, but I suggest you clean your car battery corrosion with baking soda.
But, the first thing you must do to keep corrosion away from your car battery is to clean the battery on regular bases.
6. Car’s Headlights On
We need to have car headlights on to be free and safe driving on the road, but car headlights drain a significant amount of charge from the battery.
Automobile car headlights can draw 7 to 11 amps of current from the battery, which is a huge amount compared to other components on your car.
So, now you know why car headlights draw more battery power than you think.
Letting car headlights on for a long period of time is one of the common things that vehicle owners overcome simply.
But, if the car’s headlights are on unnecessary, this can drain a car battery when the car is off.
Especially, I often notice car owners keep the headlights on even in parking, which damages the battery in the long run.
When the car is running, headlights are on, which is normal because running cars charge the battery at the same time.
But, you must avoid headlights on when it’s unnecessary to stop your car battery from draining.
7. Car Battery Too Old
Old car batteries cause various issues in a car, and excessive draw on the battery is one of them.
Car batteries need to be replaced after a certain period of time, but replacing the battery also depends on battery use and other factors.
On average, a car battery can last between three to five years after that battery must need to be replaced.
Too old batteries face difficulty holding charge; that’s why your old battery goes dead more quickly than a new car battery.
Finding how old your car battery is easy; most battery manufacturers stamp the date code on the top of the battery.
As an auto mechanic, I always suggest car owners replace the car battery after three years.
Therefore, you must replace your car battery when it’s too old; otherwise, the battery goes dead even when the car is off.
8. Charging System Failure
Car charging systems deliver electrical energy to power the car while it’s running. That’s why a proper charging system is essential for every vehicle, not only for cars.
In several cases, I often see car charging system failures drain a car battery when it’s off.
If your car has a charging system failure, your car battery won’t be able to get sufficient charge to supply power to the car.
As you know, car batteries also charge when the car is running. But, if the car has an obstacle in the charging system, it won’t be able to charge.
Detecting the car charging system failure is a little tricky and might require experts.
After noticing a charging system failure in your car, you must take action as soon as possible to stop your car battery from draining.
How Do You Stop A Car Battery From Draining When The Car Is Off
You must take steps to stop your car battery from draining when it is off because if the car battery drains constantly, it will be replaced sooner than you expect.
See what to do if the car battery is drained when the car is off:
- Run parasitic draw test:
Whether you are battery draining when the car is off, or the battery won’t start the engine, running the parasitic draw test is necessary. Below I show the step-by-step guide on how to run a parasitic draw test on the battery. You can also follow that.
- Park your car at a stable temperature:
On a sunny or hot summer day, park your car in a shady area where the temperature is normal and suitable for your car battery. Same with cold temperatures, make sure you park your car in the garage in winter.
- Use a trickle charger:
If you let your car sit for a period of time, charge your car battery with a trickle charger which will stop your car battery from dying.
- Avoid unnecessary car battery draw:
by avoiding unnecessary draw on the car battery, you can easily stop your car battery from draining when the car is off. Unnecessary car accessories always drain the car battery even when the car is not running.
- Regular car battery inspection:
The car battery needs to be checked several times a month. Whether you drive an electric car or a petrol car, you must do an inspection regularly. Check your car battery for corrosion, loose connection, battery leaking and more which is what you should do if the car battery is drained when the car is off.
Related Article: Why Car Battery Sparks When Connecting
Perform Parasitic Draw Test To Detect What Can Drain A Car Battery When The Car Is Off
You also need to perform a parasitic draw test to detect what can drain a car battery when the car is off; that’s why here I’m going to show you how it’s done.
A step-by-step guide to performing parasitic draw tests on the car:
Step 1: Ready Your Car For Parasitic Draw Test
The battery should be fully charged, and everything must be shut off in the vehicle.
You can also leave your car for a couple of minutes to go to sleep mode before performing the parasitic draw test.
Step 2: Disconnect Your Car Battery
Make sure you disconnect the negative battery cable from the negative battery terminal.
If you haven’t disconnected car battery cables before, you can get help from your neighbor or friends.
Step 3: Connect The Multimeter
Bring a multimeter that is operating and also working properly. First, connect the multimeter’s red probe to the negative cable of the car loom. And the black probe to the negative battery terminal.
Step 4: See The Reading on Multimeter
After making a connection between the battery and the multimeter, you are going to see the reading that tells whether your car battery has a parasitic drain or not.
If the reading is more than 50 milliamps, that means any car components are draining too much power from the battery.
Between 20 to 50 milliamps are completely normal; that says your car battery does not have a parasitic drain.
Step 5: Check the Fuses Box, If Multimeter Reading Higher Than Normal
When you see the Multimuter showing over 50 Milliamps reading, that means your car battery has a parasitic drain.
Under the hood of your car, you will find the fuse box that you need to pull out while the multimeter is connected to the battery.
Step 6: Find Out The Affected Fuse
To find what component of your car drains the battery, you need to pull fuses from the fuse box.
During pull fuses, notice the multimeter reading. You must stop if you find a fuse that makes the reading drop significantly.
A fuse that drops 3.03 amps to 0.03 amps is the fuse that drains your car battery when the car is off.
Find out what car components are powered by that fuse that drains the battery.
On the owner’s manual, you find the diagram where every fuse’s details are listed, which tells you what component is connected with that circuit.
Repair or replace that car component as soon as possible to stop the parasitic drain on your car battery.
Step 7: Disconnect The Multimeter And Reconnect The Battery
Now, you just need to disconnect the multimeter and reconnect the battery as it was before.
If you do not have a multimeter and also experience, you can get professional help.
Can An Alternator Drain A Battery When The Car Is Off?
Yes, an alternator drains a battery when the car is off, especially if the alternator is defective. A bad alternator can allow electrical mishaps to drain the battery.
Noticing an alternator that drains the battery is quite confusing and also requires some expertise.
But, if you let the alternator drain your car battery, this is going to make your battery dead completely.
So, it’s necessary to maintain the alternator so that the alternator can not be a cause of draining the car battery.
To tell what can drain a car battery when the car is off, you must run several inspections on your car battery and in the car.
Excessive draw on the battery is not applicable for any type of car battery. Vehicle car batteries need to recharge when the car is shut off.
Bad alternator, corrosion, and parasitic draw are the possible causes that drain a car battery when it’s off.
Performing parasitic draw tests on the car battery can help you find out what can drain your car battery when your car is off.
Follow this guide to see what drains your car battery and how to stop it.
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I’m Meraj Sarker. I am a Car Mechanic and a student of Automobile Restoration here in Florida, USA. I’ve been studying automotive for around 9 years now. So you can rely on my recommendation. For me, studying and getting knowledge about automobile it’s really fun and entertaining. I will help you to get solutions for your car through this website. If you need any help let me know.