# 10000mAh portable USB charger \$13

At the very least you need to reduce that by 20%. USB batteries are about 80% efficient at most.

Okay, Iām taking crazy pills this morning, apparently. iPhoneās take about 1A to fully charge at 5V so it would actually be 10 full charges.

Well, bullshit aside, I mean. I think we can safely assume a bunch of bullshit. I donāt think Iāve ever used a battery that lasted as long as it said it would. Many donāt seem to do half.

And 10 - 20% = 8, which is what I said initially! (Not that it even is what I said initially, butā¦ uhā¦ look over there!)

10,000/1,440=6.94, not 8. Reduce 6.94 by 20% and you get 5.55 - consistent with what the #2 Amazon review by Yougotit says, that they get 5 iPhone 5 recharges from the unit, plus a little left over.

You have to read what @JeffreyM said to me and my subsequent response. My first calculation was total bullshit because you canāt just convert mAh in one battery to another when they output different voltages. In the real world, USB charging an iPhone 5 takes 2 hours and 5V and 0.5A, so it takes 1Ah at 5V which is one tenth of the battery. Initially I said it would multiply your battery life by 8, which is to say it will add 7 times the battery life to it (6.94). Hence, 10 (real number of charges) - 20% = 8 which is how I phrased my initial answer of 7.

Plus, I misread what @Shaddack said above to top things off.

Basically, you could just replace all my posts with, āWell, Iām pretty dumb, but 10,000mAh sounds like a lot!ā

(But I stand by 10Ah, what the hell is up with thousands of milli-things?)

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Thatās a lot of math. Why canāt all batteries be rated in a new unit iPc ::= iPhone charges?

Iād prefer they be rated by how long and how hot they will burn when they spontaneously combustā¦

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Why donāt you just call it a 10Ah portable USB charger?

Most electronics that are āfulfilled by Amazonā or directly sold by Amazon cannot ship to Canada from Amazon.com.

As for the item in the OPā¦ Iām always wary of mAh claims in general, but Iāve had good luck with this one, which does have free shipping to Canada but isnāt quite as cheap.

Why donāt you call it a 50WHr portable USB charger?

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