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Like many people who use their car regularly, I like to charge my phone when I'm driving so that it isn't flat with I get to wherever I'm going. I know that some computers have a fast charge port specifically designed to charge such devices.

If I am only going a short distance and have forgotten to charge my phone overnight, or it has been subject to heavy usage or whatever else the case may be, I would like to be able to maximise the amount of charge my devices will get.

How can I charge my phone using an in-car charger as fast as possible?

In other words:

  • How do the alternator, transformer and battery each affect the rate of charge respectively (if at all)?
  • Do you have any tips for fast in-car charging (or how to avoid it being unnecessarily slow)?
  • Is there any way to charge a phone or tablet faster through the car than a standard USB port adapter like this one?

Car Charger

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The charging system of a car can deliver TONS of power, so small fluctuations in the alternator or battery are going to be meaningless to the comparatively small amount of power a phone charger needs, so I'm going to say "no effect at all" here.

Different models of USB chargers will put out a different amount of power, normally labeled in Amps or Milliamps. The USB specification for a computer says that you must supply 500mA (0.5A) of power. Laptops that have a special charging port allow up to 2A of power through that one USB port. Similarly, you can find car chargers that output anywhere from 250mA to 3A. (To get as low as 250mA, I'm assuming a $2 device labeled as 500mA that performs poorly, but they do exist, and people do expect them to work as well as a nicer model...)

So, the best tip is to get a quality USB charger, and enjoy.

Note about iPhones and iPads

Of course Apple has to be different... If the phone or tablet can't "detect" that it is connected to a high-amp charger, it will charge at a very slow rate. If you have an Apple device, make sure the charger says it's compatible with iPad/iPhone to make sure you get the best charging speed.

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The car/battery/lighter socket does not matter, it is the lighter socket to USB adapter. These are typically limited to 5v, 500mA. You might be able to find one for your phone that allow a higher voltage / amperage.

Another option is to use a power inverter that converts 12v DC to 120V AC and use the AC charger that came with your phone.

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    These days it's pretty easy to find 12V USB chargers that output more than 500 mA.
    – Nate Eldredge
    Jan 30, 2016 at 0:56
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    Confirming what nate says, I have several 1A and 2A usb chargers at home.
    – Martin Argerami
    Jan 30, 2016 at 5:40
  • You definitely don't want a device that delivers a higher voltage!
    – guntbert
    Jan 31, 2016 at 16:35
  • My Maxx II can use up to [email protected]. It all depends on the phone. The charger would need some logic to communicate with the phone as the home charger does.
    – rpmerf
    Feb 1, 2016 at 11:16

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