What Drains a Car Battery

by Phil Borges // in Car

A car battery is what provides the electrical current that starts your engine and powers the accessories in your car. Without a healthy battery, your car simply won't run. So, what drains a car battery? Keep reading to find out the most common culprits.

What drains a car battery?

A car battery is drained when the electrical current flowing from the battery to the starter motor is greater than the current flowing back from the motor to the battery. This can be caused by several factors, including:

Overuse of accessories (e.g., lights, radio, heat/AC) - The battery supplies power to all of a car's electrical accessories, and if any of these are left on for too long, it can drain the battery.

Faulty wiring or connections - Faulty connections or loose wires can cause a "leak" in the electrical system, which will gradually drain the battery.

Parasitic draw - A parasitic draw is an electrical current that "leaks" even when the car is turned off. This can be caused by many things, including a faulty alternator, an aftermarket alarm system, or a stuck relay.

Corroded battery terminals - If the terminals on the battery are corroded, they may not make a good connection, which can cause a drain.

A bad Alternator - The alternator is what charges the battery while the engine is running, so if it is not working properly, the battery will eventually be drained.

Leaking battery - If the battery leaks, the electrolyte inside can drain out, causing the battery to lose its charge.

The battery is too old - As batteries age, they lose their ability to hold a charge, so an old battery is more likely to be drained.

These are just some of the potential causes of a drained car battery. In order to avoid draining your car battery, it is important to be aware of these potential causes and take steps to prevent them.

What causes the battery to drain in a car overnight?

One most common reasons is leaving the headlights on. The battery will also drain if the dome light is left on or if there is a short circuit somewhere in the car. A number of small draws can also slowly drain the battery over time.

Another reason a battery may drain overnight is if the car's parasitic load is high. Parasitic load is the electrical current that a battery must supply to keep all of the car's electronic systems running, even when the engine is off.

There are several things that can cause parasitic drain, including short circuits or electrical devices that remain energized, like under-hood or glove-compartment lighting, headlights, the computer module, or trunk lighting. Another possibility is relay switches that remain powered even when the car is turned off. If you suspect you have a parasitic battery drain, the best thing to do is take it to a mechanic and have them check it out.

Can a bad car battery drain itself?

Car batteries are essential for keeping your vehicle running, but they can be finicky things. If you don't keep an eye on them, they can suddenly die on you. And, if your charging system isn't working properly, your battery can drain itself even while you're driving. Most cars power their lights, radio, and other systems from the alternator, which makes the battery drain worse if there's a charging problem. So, if you're having trouble with your car battery, it's important to get it checked out as soon as possible. Otherwise, you might find yourself stranded on the side of the road with a dead battery.

How do you stop a car battery from draining when not in use?

A car battery will slowly drain even when the car is turned off, so it's important to take some steps to prevent this from happening. One way to do this is to use a trickle charger or battery conditioner, which will keep the battery charged even when it's not being used.

Another way to prevent the battery from draining is to avoid turning your car on and then off again within a short period of time; this puts a strain on the battery and can cause it to lose power more quickly. If you need to make a short journey, try to drive for at least 15-20 minutes so that the battery has a chance to recharge itself. And if you have more than one vehicle in your household, alternate trips so that one car isn't being used all the time while the other sits idle.

By taking these simple precautions, you can help extend the life of your car battery.

Can an alternator drain a battery?

Let's say your car has been sitting for a while, and you go to start it up. The engine turns over, but the car won't start. You pop the hood and notice that the battery is dead. Odd, you think - the alternator is supposed to keep the battery charged. So what happened?

It's possible that a problem with the alternator caused it to drain the battery. Alternators are complex pieces of machinery, and there are a lot of things that can go wrong with them. If something isn't working correctly, it can cause a draw on the battery, eventually leading to a dead battery.

If you suspect that your alternator might be draining your battery, the best course of action is to take your car to a mechanic and have them take a look. They'll be able to diagnose the problem and get your car back up and running in no time.

Can a blown fuse drain your battery?

If you've ever had a blown fuse, you know it can be a real pain. Not only does it mean that your circuit is interrupted, but it can also be tricky to track down the source of the problem. However, one question often arises is whether a blown fuse can drain your battery.

The short answer is no - a blown fuse will not drain your battery. However, if you have a battery that is already weak or damaged, it may struggle to power your car's electrical system, which can eventually lead to a dead battery. So if you're dealing with a blown fuse, be sure to check your battery as well. With a little troubleshooting, you should be back on the road in no time.


There are different factors that can drain a car battery. That is why it's important to be aware of what they are so you can avoid them and keep your battery healthy.

The most common culprits are lights, the stereo, and accessories that are left on when the car is off. Driving in stop-and-go traffic or in extremely cold weather can also take a toll on the battery. Urgent attention to these factors can help you extend the life of your battery and avoid being stranded with a dead one.

About the author, Phil Borges

Phil Borges is a battery aficionado. He's written extensively about batteries, and he loves nothing more than discussing the latest innovations in the industry. He has a deep understanding of how batteries work, and he's always on the lookout for new ways to improve their performance.