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I was in an electronics store and needed to know if any of their powerbanks would charge my 2019 MacBook Pro. The powerbanks outputted 20 watts, and I know if a MacBook is provided with too low wattage, it simply won't charge, but I don't know if that minimum is above or below 20W.

Question

Most powerbanks will provide some info like this:

enter image description here

Is there a general way to find out if this meets the requirements to charge a particular MacBook? For example, by looking up system settings, or via some online resource?

Note:

  • This question isn't about a specific model MacBook (neither the one mentioned above, nor any other specific MacBook, for example this one), but purely a solution in the general sense (i.e. one that can be used for all/any MacBooks - like an online resource or way of looking this value up in system settings).
stevec
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  • Magsafe or USB-C? There's really little tolerance for voltage, it has to match what the device wants. USB-C bypasses this by being 'smart'. – Tetsujin Nov 09 '22 at 18:49
  • @Tetsujin I only have USB-C on my MacBook. I think the fast charge feature uses 96v, but that it can accept much lower, but not too much lower. But I just don't know what those values are nor how to find them. – stevec Nov 09 '22 at 18:51
  • I very much doubt any portable device is going to be wanting 96v. That's barely below US mains voltage. – Tetsujin Nov 09 '22 at 18:54
  • @Tetsujin maybe I'm mixing up voltage and wattage – stevec Nov 09 '22 at 18:55
  • @Tetsujin I just checked a photo I took of the powerbank packet, and it's indeed wattage (the figures are correct, just the metric that's wrong). I'll update – stevec Nov 09 '22 at 18:56
  • Not a wise thing to do ;) Amps = Volts x Watts As a general rule [which 'smart' USB-C kind of works around] Volts must match, amps/watts can exceed spec, because they are 'pulled' not pushed. Volts are 'pushed', which makes exceeding specified voltage unwise to dangerous, depending on how far you exceed. – Tetsujin Nov 09 '22 at 18:57
  • @Tetsujin I added a pic of the packet of the powerbank. Would be super handy to know which metics I need to be concerned about (e.g. voltage, wattage, or both), and how to find whether a MacBook is compatible with that power source. – stevec Nov 09 '22 at 19:02
  • I just realised it's probably a duplicate of How to determine if a USB-C power bank can charge my macbook? – stevec Nov 09 '22 at 19:08
  • See https://support.apple.com/en-gb/HT201700 - you also need to know how long it can provide that charge for. Basically, a 20W supply is going to be under-spec. – Tetsujin Nov 09 '22 at 19:13
  • @Tetsujin thanks, it's easy to tell the adaptor that comes with the mac, it's just hard to tell what it will accept at a minimum (the one it comes with is: "Apple 96W USB-C Power Adapter and USB-C Charge Cable" - 16-inch MacBook Pro models introduced in 2019). That is, I'm confident the MacBook will still charge with much less than 96W, but I just don't know precisely how much less. – stevec Nov 09 '22 at 19:17
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    Depends whether you're using it or powering down & charging overnight. If you're using it, don't expect 20w to even vaguely keep pace. – Tetsujin Nov 09 '22 at 19:36

1 Answers1

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I’ve used 5 volt 2.1 amp USB-A charger with a USB-C cable for M1 Max MacBook Pro 16.

I suspect anything 5 watt plus will work.

Here is an on topic YouTube video.

To be very clear, at less than 15 to 20 watts, your battery may drain faster than it can be charged if the computer isn’t idle.

This command tells you the current power draw:

sudo powermetrics -i 1000 -s cpu_power,gpu_power | \
    egrep '^Package Power:|^GPU Power:'

You will likely lose 5 percent of the charge efficiency. In my testing while typing this, my M1 Max used about 500 mW to 961 mW. That is about 1 watt. So a 5 watt iPhone charger would maintain my current power level. If you are using significantly more power, you will want a much higher power output like the 20 watt to 96 watt chargers.

@gidds also recommended a menu bar app to determine power draw.

James Risner
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  • All USB charging is 5v, and as Tetsujin correctly points our earlier: a 20w charger won't keep up if the computer is on. A 5w charger will indeed put power into the battery, but only if the computer is shut down, and then only very slowly. – DavidRecallsMonica Nov 09 '22 at 23:50
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    Another way to see the power draw in real time is with a menubar tool such as iStat Menus. (FWIW, my 16" MBP idles at around 4W with only an external monitor, and 10W using its own screen, though that depends a lot on the brightness; the screen backlight is a major power sink.) – gidds Nov 12 '22 at 16:39