How to know the charging/discharging speed of your MacBook

I recently encountered this problem when the charger of my MacBook 11” was stolen in the library. I had to use a USB charger for my Samsung Galaxy to charge the laptop with a micro-USB to USB type C converter. Obviously it wasn’t quick enough so the net effect on the battery was discharging. I have a few phone chargers, and a portable battery, so I would like to know the charging/discharging speed.

After some Googling I found the system command system_profiler. It lists all the system information about your Mac. To follow the following instructions, you need to have Terminal (Launchpad-Other-Terminal) opened.

First I’ll use a MacBook Pro 15”, mid 2015 as an example of displaying the discharging speed.

The charging/discharging speed is basically indicated by the battery current. If it’s negative it means your battery is discharging and vice versa.

I fully charged the laptop and waited until the battery went to 99%. I then did

system_profiler SPPowerDataType

and saw the following information about the Battery.

Notice the Amperage (mA) and keep in mind that it might change a little based on your activities but it should always be negative if you don’t connect to a charger. You should repeat this a few times to get a rough estimation about the basic power consumption of your laptop. If you don’t want to see so much information but only the Amperage, use

system_profiler SPPowerDataType | grep -I "Amperage"

Typically there will be some delay but it doesn’t matter. See example below

Now if I connect the charger (85 W) it shows a positive Amperage indicating a fast charging

The estimated Amperage of a MacBook 11”, with minimum activities (only Chrome opened and no “significant energy usage”) of different chargers are:

  1. A Samsung Quick Charger (for Galaxy S7 edge) + nanoUSB cable + nanoUSB to USB C adapter: Roughly -200 mA. Even though you turn off the laptop, charging speed is super slow.
  2. A Samsung Quick Charger (for Galaxy S8 edge) + USB C cable: Roughly 0 mA (so if you turn off the laptop it should be charging quickly enough).
  3. A Samsung normal charger (for Galaxy S6 or earlier) + nanoUSB cable + nanoUSB to USB C adapter: Roughly -300 mA. Even slower than 1. Almost not visibly effective charging.
  4. A portable battery, marked up to 5 A: Roughly -100 mA. Slow but useful.

So, if you lost your original charger, you may use a Samsung USB C charger and its cable and shut down your computer for temporary rescuing. Or, you have to buy a good charger from Amazon…