It's a cell phone no-no, but odds are, you do it every day!
Does Charging Your Phone in Your Car Drain Its Battery?
Updated on May 12, 2025
Whether you’re a homebody who must have the GPS running in order to avoid getting lost or you’re someone who takes their role of being a passenger DJ seriously, a low phone battery can throw a wrench in any car ride. Reaching for that USB port might feel like a quick fix, but is it really as harmless as it looks? Some claim it’s too slow, others worry it’s bad for your phone. And then there’s the big question: Does charging your phone in the car drain the battery?
We reached out to Joshua Sutton, manager of the training department at tech repair franchise uBreakiFix, and Bradley Nichols, director of operations at Staymobile, another technology provider offering mobile and desktop device repair and protection in New York, to tell us more about what happens when you use car chargers to power up your phone. Read on to learn exactly why charging a phone in the car can drain its battery and how you can use a car charger without letting that happen.
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How charging your phone in the car drains its battery
Believe it or not, frequently plugging your phone into the USB car charger poses a serious risk to your phone (and sometimes even your car). Here’s how it happens:
- Inconsistent power supply: Most cars come with a cigarette charger (also known as a cigarette lighter), which generally provides a 12V power outlet. “Smartphones typically use 5V when charging, which the adapter is normally able to safely regulate for the voltage,” Sutton told Reader’s Digest. “However, if the adapter is malfunctioning or is not made by your phone’s manufacturer, it can send too much power to your smartphone and potentially damage it. Most of the time, you may not immediately notice this damage, as it generally affects your phone battery first, diminishing the health of the battery,” he adds.
- Quality of the charger: Beyond voltage, chargers vary in build quality and safety features, differences that can impact your phone’s performance and longevity. Low-quality or uncertified ones often skip safety features that protect your phone from overheating, overcharging or short-circuiting—risks that can shorten your phone’s life. Even though you may not notice the damage to your phone immediately, exposing it to such conditions could be an expensive cost in the long run. “The worst-case scenario is that it could damage your phone’s charge port or the motherboard itself, a very expensive proposition,” says Sutton.
- Overheating: Charging your phone in a parked car—especially under direct sunlight—can lead to serious overheating. This excess heat affects both your phone and its battery, potentially causing long-term damage.
How to use a car charger safely
Even if you try your hardest to make your phone charge faster before leaving home, those 15 minutes can only do so much. And unless you’re carrying a power bank, sometimes you just have no choice but to plug your phone into the car to charge. (We all know how nerve-wracking that low-battery sign can be.) But if you have to use your car’s charger, there’s a safe way to do it. Keep the following tips in mind when charging your phone in the car:
- Use certified chargers: “A good rule of thumb is to always use your phone manufacturer’s official car charger to ensure the highest quality and proper power regulation,” recommends Sutton. If you’re still concerned about power output, Sutton recommends investing in a power inverter for your car, with the Pure Sine Wave Power Inverter being his first choice. “It can detect any rapid changes in power output from the car’s power outlet (or cigarette lighter) and safely regulate the power your smartphone receives,” Sutton says. “They are larger than traditional car chargers but are infinitely safer. It also has the added benefit of often coming with AC power outlets built in to provide power to laptops as well.”
- Regularly inspect the adapter and cords: Damaged cords and chargers aren’t just annoying—they’re risky. Exposed wires can cause short circuits, overheating or even small electrical fires, putting both your phone and safety at risk. Experts suggest that it’s best to do a bit of research into your vehicle and the cords you’re using. With the right equipment, the potential for such mishaps goes down and so does the fast battery drainage.
- Be cautious of overheating: If your phone or charger feels unusually hot while plugged in, it’s time to unplug it. Unless you’re in an emergency, charging an overheating phone does more harm than good—give it time to cool down first.
Most important, remember that it’s not safe to use your phone while operating a vehicle. “Anytime a person’s hands leave the wheel or eyes leave the road, it becomes incredibly dangerous for them and the other people around them,” says Nichols. Bottom line: Play it safe, do your research and wait until you get home to plug in.
FAQs
How long can you charge your phone in the car before the battery begins to drain?
It’s a common phone battery myth to think there’s a “safe window” for car charging. Battery health degradation is usually a slow process that affects your phone over time. Yes, using the car charger once in a while is OK, but doing so frequently—even for short amounts of time—can still be detrimental to your phone’s battery health.
Do car chargers drain the battery when the car is off?
Yes—and not just your phone’s battery but the car’s too! According to a report by The Sun, charging your phone in the car can drain its battery. But while that’s a much slower process, it is your car’s battery that’s affected first. Your car battery can handle a quick phone charge, but if the engine’s off, there’s nothing to refill that lost power. Do it frequently enough (especially with an older battery), and you might find yourself stuck with a dead car and a fully charged phone (that probably took way too long to get to 100%).
About the experts
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Why trust us
Reader’s Digest has published hundreds of articles on personal technology, arming readers with the best tips, tricks and shortcuts for computers, cell phones, apps, texting, social media and more. For this piece, Brooke Nelson Alexander tapped into her 10-plus years of experience covering the latest in digital trends, product reviews, cybersecurity and privacy to ensure that all information is accurate and offers the best possible advice to readers. We rely on credentialed experts with personal experience and know-how as well as primary sources including tech companies, professional organizations and academic institutions. We verify all facts and data and revisit them over time to ensure they remain accurate and up to date. Read more about our team, our contributors and our editorial policies.
Sources:
- Joshua Sutton, training department manager at uBreakiFix
- Bradley Nichols, director of operations at at Staymobile
- The Sun: “FLATLINE: ‘That’s going to have consequences,’ warns expert over common item left in cars that can drain the battery flat“
