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Short post day – charging laptops with weak chargers

How long would it take to fully charge my Mac from 0 to 100% with my 5 W charger?

Why this question? Well, I have a cheap Chinese power bank that claims a battery capacity of 10,000 mAh. No doubts whatsoever. This is most definitely a 10,000 mAh power bank:

Apple 5W charger for scale

OK maybe it’s not 10,000 mAh but we all expected that. It’s even slimmer than the 5W charger!

And the manufacturer didn’t lie only about the battery capacity – they lied about the capability as well. It says 5 V 2 A output on the bottom, but with my USB tester it only supplies 5.1 V at 0.95 A – which is about 5 W if rounded up.

Pull up the MacBook Pro 15″ 2018 spec sheet, and you get this:

Ugh. Watt hours. Thankfully we can figure out the mAh rating if we know the voltage of the battery, and iFixit has done the hard work for us: 11.4 V. Now I don’t have to disassemble my Mac.

83.6 * 1000 / 11.4 = 7,300 mAh, give or take. Don’t like math? Use a calculator!

So this power bank can charge my laptop completely once, and partially after that? No doubt. But we want to see how long it would take.

7,300 mAh / 1,000 mA = 7.3 hours. Make it 8 hours, because you also need to consider efficiency and charging is not a perfectly efficient process.

…I think I’ll just stick to my USB-PD power bank.

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