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Here’s why the USB port built into your car charges so agonizingly slow

Jeremy Kaplan
USB Car Charger Hardly Works
USB Car Charger Hardly Works

There’s a USB port on the center console of my 2015 Mazda3, right beneath the stereo — it’s really well located. Get in the car, plug in your cell phone, turn the key (well, push the button) and you’re off.

That’s how it should work, anyway.

In reality the port is useless: It supplies about half an amp of charging power – far less than I need to juice my phone. If I start using the GPS while driving the power depletes even faster. I may as well not charge the phone at all.

For reference, the travel adapter I’m using with the amazing Galaxy S8 delivers 2.0 amps, as does Samsung’s wireless charger. The S7 had similar power requirements. Even the Galaxy S6 adapter put out 0.7A a couple years ago.

I complain about that stupid USB port every time I get in the car (my wife loves travelling with me these days). But Mazda is hardly alone here. According to mobile accessory maker Ventev, most cars have USB ports that are insufficient for our needs.

“The USB ports in your car seem like a convenient feature, but often don’t provide enough power to charge your device while using it. Instead, they often only slow the speed at which your battery drains — your phone will use power faster than the car USB port can supply it,” the company wrote in a recent blog post. Car manufacturers are beginning to install higher powered USB ports inside vehicles, Ventev added, but the instances are fairly rare. “The only exception we know of is one Acura model that advertises 2.4 amps in its USB ports, which would charge your phone just fine.”

A phone plugged into a USB port in a car — USB Car Charger Hardly Works
A phone plugged into a USB port in a car — USB Car Charger Hardly Works

How-to Geek confirmed that finding: “We measured multiple vehicles with a USB voltage/amperage meter and found that the data port in the dash (commonly used to hook up a USB drive or phone to play music) offered a very weak 0.5A output. While that’s enough to power your USB drive full of MP3s, it’s barely enough to trickle charge an iPhone and maintain the current battery level—if you’re using the phone for navigation, a notorious battery hog, it’s unlikely you’ll even charge it faster than it drains.”

USB ports designed for data transfer are passably utilitarian, I suppose – or were, a decade ago when I had a USB stick with all of my MP3 files on it. (Yes, I used MP3s back in the day, not FLAC files. I have no regrets!) But today’s phones do so much more, and few modern music listeners rely on MP3, thanks to the rise of streaming music. So why on Earth do car makers make it so hard for us?

I needed answers, so I put the question directly to Mazda: Watts up? (Sorry.) Why wouldn’t you design this port with sufficient power? Isn’t phone charging a pretty basic use case here? Do you hate me?

The company confirmed that its port supplies just 500mA of current – and pointed out that it does exactly what it’s supposed to do.

“The official international charging/power output specification for USB 1.0 and 2.0 devices is 500mA of current,” explained Mazda’s HMI and infotainment engineer Matthew Valbuena. “Mazda Connect utilizes the USB 2.0 specification and as such, our system provides 500mA of charging current on each USB port.”

Valbuena also noted that when an Apple device is connected, the USB port will provide 1A of current (as required by Apple certification – weird, right?).

why your usb car charger hardly works at all gettyimages 637185988
why your usb car charger hardly works at all gettyimages 637185988

“At rest, the system should provide enough current to charge the Galaxy S8, but if the phone is being actively used (navigation, Bluetooth audio streaming, calling, etc.) the Mazda Connect USB ports will not be able to sufficiently charge the S8’s battery to overcome the drain that the phone’s processes are incurring,” he added.

Frankly, the ports in my car don’t even supply enough current to charge my phone at rest, regardless of what the engineers think.

The issue is, Mazda and most other car makers rely on a specification finalized in April of 2000 that’s clearly insufficient for modern needs. Dig deeper and you’ll learn about addendums and extensions to the USB 2.0 spec made over the years by the group that controls it, the USB Implementers Forum.

Of particular note is Battery Charging Specification 1.2, released in 2010, which created a distinction between standard ports for transferring info and what it calls “Charging Ports,” allowing devices connected to such ports to suck up to 1.5 amps (and mandates that they can handle even higher currents). So Mazda is technically correct, but come on – gimme a charging port!

Anyone with a computer will note that there’s a newer solution of course, which has the same ability to charge our stuff and boosted transfer speeds to boot.

But keep in mind that USB 3.0 was dreamed up before the modern era too — 2008 to be exact. And since we rely on our smartphones these days for, well, everything Valbuena listed earlier, an aftermarket car charger is almost a requirement of car ownership. Where can you plug it in to get the energy your gadgets so desperately crave?

Say it with me: the cigarette lighter.

The de facto electrical connector in your car is the 12 Volt cigarette lighter (here’s a few of the best chargers we’ve found), which feels almost exactly like digging in the closet for the projector to show off slides of your latest cruise. Cigarette lighters are old news. It’s 2017. Can’t we do better? High-powered USB ports are a step in the right direction, but I’m hoping to find an inductive charging panel or bucket in the center console of my next ride.

GM offers wireless charging on a handful of cars, notably the 2016 and newer GMC Sierra, Yukon, and Yukon XL, but the panel works only with a handful of phones — and notably NOT with the Galaxy S7, S8, Note 5, and 7. Apple users are out of luck, too. The iPhone 6 Plus and 7 Plus are too big, the company warns. So … yeah, choose your phone wisely, I guess.

Other companies are on board the inductive charging bandwagon as well, including Toyota, which includes it as an option in the 2017 Toyota Prius Prime.

Are decent charging and wireless charging must-have features? Not yet. But is it something I think of every time I plug in my cell phone to the cigarette lighter in my car? You’re damn right it is.