A little meter that shows the big differences in charging plugs and cables

The Practical Meter shows you the nerdy truth about which USB thing charges which USB thing faster.

The brilliant thing about the Age of Almost-Universal USB Power (AAUUP) is you can get power from almost anywhere: a laptop, a wall plug, a portable battery backup, your car, maybe your bike—anywhere there's a little rectangular slot and a cable.

The tough thing about the AAUUP is that you are not aware of just exactly how much power is passing through to your phone or other device. Would you be better off charging through your laptop, right in front of you, or is it worth plugging directly into an AC plug? And does the cable that came with your Kindle work just as well as the one that's back at home? Maybe you don't think about this much, but you probably think about how stupid batteries are, every time your phone is dead.

Power nerds (and I am certainly one of them), take heart: the Practical Meter has arrived, fresh off a successful Kickstarter campaign ("successful" as in 16 times their goal). It works, and it will surprise you with just how different your myriad charging options can be.

Why isn't one USB just like another? The short version is that different device makers stick to different standards, and that gadgets sometimes ship with the cheapest cord or wall charger that will work for that particular device. The slightly longer version is how Practical Meter pitches itself: some computers send out power at entirely different magnitudes, and some cables have built-in circuits to carry as much juice as possible to your device. The really long version involves parsing the "Power" section of Wikipedia's page on the USB standard. With iOS 7 and Apple's certified cables, it gets even trickier.

All those differences are not small: they result in charging time differences that add up to hours. Hours in which you're waiting to call back your spouse and inform them that you're not dead in an alley. Always in fear of such a noir-ish fate, I backed the Practical Meter, received my unit last Friday, and have been playing "How many lights" ever since. Here is how it works.

You plug in the Practical Meter and, if you see a red light, that means there is some kind of power available. Good!

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Power Meter, reporting for duty

Next, you plug a cable into the Practical Meter. The Meter team actually sells a fast charging cable that they ensure will pass along as much power as possible to your device (and which came with most of the Kickstarter rewards). Plug in that cable, then plug in your micro-USB, mini-USB, or 30-pin Apple device, and you will see how many watts are passing through, represented in blue LED bars. Most devices charge at between one to five watts; for those 6-10-watt charges, the first bar alternately blinks blue and red. Here are my USB headphones charging from my laptop.:

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Only two bars (watts), but maybe that's all these little guys need.

How different can a USB cable be? Funny you should ask. I have this little 6-inch white cable I like to carry around in the front pocket of my bag, for convenience's sake. Plugging it into the Practical Meter, it shows 2 watts passing from my ThinkPad to my HTC One. Plug in the Practical Meter's cable, and suddenly there are 4 watts. That's no small thing.

The same goes for the difference between laptops and wall plugs. An iPhone 5 plugged into my laptop garners 3 LED lights/watts:

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iPhone 5 charging off a laptop at sub-optimal speed.

Plugged into an official Apple wall charger and a standard AC plug, the phone draws 5 watts. Oddly enough, so does my HTC One, even from that same cruddy, tiny cable.

meter4_0.JPGPhoto by author.
When all else fails, plug your phone directly into the source.

You might have guessed that a straight wall plug gave off more charge than your laptop, but now you know—and you might also learn that your MacBook Pro charges at up to 10 watts, too, so an outlet isn't always necessary for your phones or tablets.

At $25, with fast-charge cable included, the Practical Meter is a tough sell to anyone who doesn't really have that many cables or laptops or phone or tablets, or care that much about having power on hand. For power and battery obsessives like your author, it is almost too much of a good thing. If you need me this weekend, I'll be counting a bunch of lights.

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