If your MacBook's battery is dead and you don't have your charger with you , there's a way to save the day. If someone else near you has a MacBook, you might be able to borrow some power until you can finish your work.
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MacBook to MacBook charging should work on most MacBook models that use USB-C. Apple has been using USB-C charging on its MacBooks for many years, and there are reports that it works on both older Intel and newer Apple Silicon.
The way it's supposed to work is that the first person to connect, using a quality USB-C cable that can handle the necessary power, is the one that receives the charge, while the second MacBook connected will be the one that provides the power.
It doesn't matter which USB-C port you use, but if things don't work as expected, switching between the ports until you find the “right” one is sometimes necessary.
See also: How to restart your MacBook Pro
In a test conducted between a 2020 M1 MacBook Air 13-inch and a 2021 M1 Max MacBook Pro 16-inch, where the power requirements are quite different, with the M1 MacBook Air shipping with a 30w power adapter while the M1 Max MacBook Pro has a 140w adapter, charging was successful.
The MacBook Pro has much higher power requirements than the MacBook Air, but even though that was the case, the Pro was charging through the Air. That doesn't mean the Pro draws up to 140w from the Air, and you shouldn't expect to charge a laptop with a very low battery this way.
A large portion of the overall output provided by the 140W charger allows the MacBook Pro to use fast charging, something you won’t do when you’re connected to a MacBook Air.
See also: Apple: Fixes MacBook battery drain issue
This can be useful in situations where you have two MacBooks and only one charger. It works best if the machine being charged uses much less power than the one plugged into the power adapter, but you can extend your battery life if the roles are reversed.
