Powering A MacBook With USB-C & An External Battery

The attractiveness of USB-C is that any external battery with a standard USB “out” port can be used to power a USB-C laptop of which there are currently two, the new Chromebook Pixel and the new MacBook.

I’ve been testing how this works for the new MacBook. As an aside, yes, you can also plus those two computers together using USB-C. I have both — when you do, the Chromebook charges the MacBook. Kind of an expensive external battery, however.

Test One

I plugged in a Zagg Sparq external battery with 3100mAh of capacity, outputting at standard USB 5 volts at 2 amps. The Mac reported that it was “Not Charging” and that the power source was “Power Adapter” rather than “Battery.” The result was the Mac drew solely off the external battery (what it called the power adapter, the same thing it would call a regular power adapter) for an hour, meaning I gained an extra hour of time before it went back to the main battery

Test Two

I plugged in a Morphie external battery with with 2500mAh of capacity, outputting at standard USB 5 volts at 1 amps. The Mac reported again that it was “Not Charging” and the power source was “Power Adapter.” It eventually died and went into hibernation, despite the fact that the power icon never changed from the charging symbol. My assumption is that an external battery needs to push at at least 2 amps for the Mac to actually draw from it. Otherwise, it seems that while it says the external battery is being used, the internal battery is instead running down.

Test Three

I used a Anker 2nd Generation Astro external battery with 64oomAh of capacity, outputting at 2amps, similar to the Zagg battery in test on. Unlike with the other tests, the Mac reported a time “Until Full” with the power source as “Power Adapter.” The Mac ran off the battery for nearly two hours, 1:50 in all, until it ran out of power. In addition, the Mac’s internal battery gained about 20 minutes of time (IE, I had about 40 minutes charge on it; when the external battery died, the internal battery was up to 1 hour of charge). That means the battery gave me total power of 2 hours and 10 minutes.


I’m still going to test some other batteries I have. But at this point, it’s becoming clear that:

  • To charge a MacBook, external batteries need 2amp output.
  • The MacBook uses about 3000mAh per hour. So use that as a rough benchmark for what you might expect from whatever batter you have

Expected time may vary based on how you set your energy consumption on your own MacBook, of course. I used the standard defaults. What you run will also have an impact. I was mainly browsing the web and doing email.

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