How to determine if a USB-C power bank can charge my macbook? I am starting to realize that I may need my MacBook battery to last longer while I am outside without having any power socket available.
My MacBook has a USB-C port used both for charging and for data.
There are many USB-C power banks available online, although it seems they are mainly used for phones, but some sellers claim that some of them can be used to charge laptops as well, including a MacBook.
How can I determine if a USB-C power bank will actually charge my MacBook, before buying it and testing it, based on the MacBook specs and the power bank specs?
And what is a &quot;reasonable&quot; capacity for a power bank used on a Mac (or laptop in general)? For example, is 20000MAh reasonable enough for an &quot;average&quot; use for an extra couple of hours, or is it definitely not enough and I need a higher capacity?
My MacBook: MacBook 10,1 (Retina, 12-inch, 2017)
Some examples of power banks online

Link1 (&quot;Compatible with MacBook Pro&quot;)
Link2 (According to two different reviews it charges laptops as well)
Link3 (It says &quot;for iPhone laptop samsung&quot;)
Link4 (&quot;Output for MacBook Nintendo Switch iPhone ...&quot;)
Link5 (One of the pictures explicitly shows it can charge laptops, and description says it can charge Macbook Air)
Link6 (Specific for MacBook Pro and quite efficient apparently)
Link7 (Another charger for laptops)
Link8 (It says it is also for MacBook)
Link9 (Same as above)
If you look at the spec sheet of your MacBook it says that the charger provides up to 29 Watts, which is roughly the maximum power draw the MacBook needs. Now regarding a power bank you would want to have a look at the maximum power [W] output is provided.
Have a look at this article or this quora post where you will find out that the maximum power over a standard (non PD port) is usually with the 7.5W with for USB 3.0. However power banks may offer a USB-C (USB-A usually doesn't offer this) Power Delivery (PD) port, which theoretically can be certified up to 100W, which for mobile power banks usually is out of reach.
From the links you posted, I think options 1, 6, 7 and 9 would work fine.

To say how long a certain capacity will help you heavily depends on what you are doing while connected to the power bank. These power banks theoretically have a much higher capacity than the MacBook, yet this charging system has inherent efficiencies. Also, when you charge the MacBook with this power bank the MacBook will think its connected to a wall plug and then apply the according power settings (so make sure to set them appropriately to extend battery life).
However, I would think you could gain up to a complete charge on a 20000mah power bank. Turning off the MacBook and charging it that way is the most efficient way.

Some ideas on how to estimate the power bank endurance.

Install coconutBattery
Check the power draw at your usual workload

That will give you an idea how fast/if at all your MacBook can be charged (e.g. the newest MBP 16&quot; charger can provide up to 100W and at peak power consumption the MBP can nearly reach that).
Coconut battery also tells you what cycle count your battery is in and how much capacity is left in it. If you then open settings and go to battery (assuming macOS 11.x) you can try to roughly estimate the increased battery life when using a power bank.