Leaving Car Charger Plugged In: Safe?

Here’s everything about leaving your car charger plugged in being safe:

Your car battery and charger determine what can be left plugged in, but most of the time it can be left plugged in.

So if you want to learn all about what happens exactly when you leave your car charger plugged in, then you’re in the right place.

Let’s get started!

Leaving Car Charger Plugged In: Safe? (All the Info)

Does Your Car Charger Drain Your Car Battery When Left Plugged In? (2 Things)

Mobile phone charging in the car.

Have you ever been on a road trip and realized there’s nowhere to charge your phone? 

Truthfully, I’ve had that happen on the way to the grocery store. 

A USB charger means no worrying about your phone dying because there’s nowhere to charge it.

A car phone charger is convenient.

And these days, new cars typically have a USB port. 

You can also get an adapter to plug into the cigarette lighter socket for older vehicles without a port.

Of course, leaving the USB cables and charger in the car makes it even easier. 

Who wants to have to remember to take the stuff with you every time you leave the house? 

Why not have a USB charger specifically to go in the car?

But do you wonder if it’s safe to leave your car charger plugged in? 

Does it drain the battery? 

Let’s find out!

#1 Car Chargers Are Convenient but Dead Batteries Are Not

Woman's car broke down.

For the most part, newer model cars and trucks can handle it if you leave a USB cable or charger plugged into an auxiliary power outlet. 

Doing so won’t drain the battery quickly.

The thing is, not all car chargers or car batteries are created equal.

For example, a 12-Volt cigarette lighter socket output fluctuates widely from car to car. 

So plugging a USB charger into it could drain the battery if the vehicle isn’t running.

Or, your battery might be old, and the energy draw could be enough to drain it.

That said, USB cables and chargers typically don’t draw a lot of energy on their own.

But you do need to think twice before leaving a device charging when the car isn’t running.

The alternator recharges the car’s battery when the car is running. 

If your vehicle sits too long without a charge from the alternator while charging your devices, it could drain the battery.

#2 Protect Your Car’s Battery

Mechanic checking battery in car

An old battery will drain and die quicker when the alternator isn’t keeping it charged. 

What’s more, cars with power seats, keyless ignitions, and remote GPS continue to use the battery when the vehicle is off.

It’s good practice to know what accessories are running while your car is off, and best to unplug chargers, USB cords, and devices if your car is going to sit for a while.

Without starting the car and engaging the alternator, there’s no way for your car’s battery to recharge.

A car’s outlet usually has nearly 12V of power when the car is off.

However, when it’s running, the voltage goes up to 13.5V-15V, as the alternator does its job.

What’s the lesson here? 

First, determine if the car’s USB port stays powered up when the car is off.

If so, don’t leave USB cords, your charger, or any other devices plugged in to protect your car’s battery.

Do the Ports Shut Off When the Car Is Not Running?

Phone charger plug on a car.

These days cars have safety features to prevent electronics from draining the car’s battery when it’s off.

But it’s not like that in older vehicles. 

Depending on the car’s make, year, and model, the USB port could keep charging when the car isn’t running.

Now, maybe you’re wondering how you can find out if your car has USB ports and connections that stay active. 

Generally, your vehicle’s owner’s manual specifies how power sources such as the cigarette lighter socket and USB ports work.

But you can test it yourself.

How Can I Test My Car’s USB Charger Power Source?

USB charger in the car.

The original purpose of an automobile auxiliary power outlet was to power an electric cigarette lighter.

Back in the day, everybody smoked. 

Nowadays, the cigarette lighter socket is an electrical power source for cell phones and other portable accessories.

Maybe your car isn’t running.

But some things remain powered, including:

  • Power locks
  • Radio memory
  • Remote start modules
  • Cigarette lighter socket

It’s simple to test if the power is still there when the car is off. 

Leave a cell phone charger plugged into the car’s USB port and check the charging bar on your phone to see if it’s active.

You can also push a cigarette lighter in to see if it heats up when the car is off. 

Typically, cigarette lighters work even when the car isn’t running. 

And, while lighting a cigarette isn’t likely to drain your car’s battery, leaving your cell phone plugged in could.

Is It Safe to Leave Your Car Charger Plugged In? (2 Considerations)

Charging a phone in the car.

There are a few other things to think about when it comes to car charger safety.

For example, having a USB cable or a car phone charger lying out in the open could attract thieves. 

Statistics show that cell phones, chargers, and other electronics are among the top items thieves steal from vehicles.

The climate is another consideration. You shouldn’t leave a USB cable or car phone charger plugged in under extreme weather conditions. 

Temperatures outside of a range of 32-90 degrees Fahrenheit (0-32 Celsius) can damage electronics.

#1 How Reliable Is Your Car Phone Charger?

Phone plugged in a car charger.

There are many manufacturers offering plug-and-play devices and car phone charges for cheap.

But, like most things, you get what you pay for—so is your USB charger reliable?

It’s best to stick with reliable brand names to ensure you get a quality product.

Also, cheap cables and USB chargers can be of low quality, which means the wires can come apart from using them. These cheap devices can potentially pose a safety hazard. 

It’s always safest to go with a manufacturer-recommended compatible device.

#2 Overcharging Can Degrade Your Cell Phone’s Battery

Smartphone charging on a wireless charger.

Up until now, we’ve thought about how the vehicle’s battery is affected by leaving a car phone charger plugged in.

But, think about your cell phone’s battery. 

While it’s convenient to leave your phone plugged in while you drive, it might not be the best choice.

You may not want to read this, but overcharging will reduce your phone’s battery’s lifespan.

If you have lots of Apps on your phone, it could take a long time to charge.

Or it could lose its charge quicker than you want.

So many of us leave our phones plugged in whenever possible.

The bottom line is that you should remove electronic devices from a charger when they’re done charging.

Leaving a cell phone plugged into the charger when the battery is full will degrade the battery.

Whether you’re charging your phone at home or in the car, it’s important to remember to unplug it when it’s fully charged to get the most battery life.


  • Theresa McDonough

    Tech entrepreneur and founder of Tech Medic, who has become a prominent advocate for the Right to Repair movement. She has testified before the US Federal Trade Commission and been featured on CBS Sunday Morning, helping influence change within the tech industry.

    View all posts