Two things are at play here: how much power your charger can supply, and how much power your phone is using while it’s being charged.
I’ll warn you: for the first, at least, you’re going to need a magnifying glass, or at least extremely good eyesight.
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Chargers vary a great deal in size, shape, and quality. But one of the most important, and often unnoticed, differences is in how much charging power they provide.
All chargers take your line voltage – typically 120 or 220 volts – and convert it to 5 volts. It’s that 5-volt side that is then connected to your device to charge it. 5 volts is not only the same on all chargers, it’s actually part of the USB standard. Power provided over USB cables is 5 volts, period.
Where things differ is in the amperage that the charger provides. That’s a measure of how much electricity, or “current,” can actually be provided through the wire at 5 volts.
As it turns out, amperage makes all the difference.
Volts and amps
Voltage and amperage are confusing concepts. An admittedly over-simplified1 metaphor looks like this:
Consider a squirt gun – typically a plastic toy that you fill with water. To use it, you squeeze a trigger to shoot the water out of the gun.
- Voltage is akin to the size of the hole that the water comes out of.
- Amperage is analogous to how hard you pull the trigger.
You can get more water out faster either of two ways:
- Make the hole bigger. (Increase the voltage.)
- Pull the trigger harder. (Increase the amperage.)
When it comes to USB connectors, the “size of the hole” is fixed at 5 volts. In a way, that means we can line up or plug in any two holes of the same size, and they’ll fit. (Perhaps you’re using your squirt gun to fill a bottle. If the holes aren’t the same size, things could get messy.)
So the only thing we can control is amperage.
The USB specification
It turns out that USB, while a very nice, albeit occasionally frustrating, standard for connectors used for USB, actually gets in the way.
It specifies that the voltage should be 5 volts, and that the amperage provided by a computer’s USB data connection should not exceed half an amp, or 500 milliamps (500mA), where a milliamp is one one-thousandth of an Amp2.
Once upon a time, that was enough. But today, while that’s enough to run many devices, it’s not really all that exciting for charging devices. In fact, it’s definitely the low end, and results in a very slow charge for many devices.
USB chargers, however, have no such limitation.
It’s up to the power adapter’s manufacturer to determine the capacity of their device3. Providing more power means using more expensive components, so many USB power adapters err on the side of “not much”.
Here’s how you can tell what you have.
Every charger has its output specifications printed on it somewhere, often in incredibly tiny print. For example: Output 5.1V (5.1 volts4) and 750mA. An adapter with that rating can provide 1.5 times the power of a standard USB data connection from your laptop. Thus, it would charge your device faster (though not necessarily 1.5 times faster, as things are rarely that simple).
Another might offer 2.0A (two Amps, or 2000mA). This charger is capable of providing four times the amount of power as a standard USB data connection. It’ll almost certainly charge your device faster.
What the device is doing at the time matters
While the charger you use can definitely make a difference as to how quickly your device charges, so will what that device is doing at the time.
Most smartphones, for example, are nothing more than small computers. They use more power when they’re working hard on then they do when they’re idle.
What does it mean to “work hard”? Well, that varies. Watching video, playing a game, running a WiFi hotspot, or just running a poorly written app on your device will use more power than when the device being charged is doing relatively little. In most cases, a sufficiently powerful charger will provide power faster than it’s being used, and your device will charge, albeit more slowly if it’s running one or more of those power-draining applications.
In the worst case, a charger may not be able to keep up, and the device will continue to use its battery, albeit at a slower rate than if not connected to a charger at all. I’ve experienced this running my phone as a WiFi hotspot (very power intensive), using only my laptop’s USB connection for power, which is the minimal 500mA. The phone lasted longer – several hours, instead of just one – but at the end of the day, the battery was still nearly empty.
Knowing what we now know, there are two things we can do to charge our devices more quickly:
- Choose a charger with a higher amperage rating for its output. At this writing, if I were purchasing a charger, I wouldn’t get anything that puts out less than 1.5 Amps. It’s quite safe to have “too much”; the device being charged will only take as much as it can handle.
- Try to make sure that the device is as idle as possible. Putting a mobile phone into airplane mode, for example, turns off all of its radios and can reduce power consumption significantly.
The net result in either case: a faster recharge.