Is your MacBook battery failing and you’re far from a charger? If there’s someone else nearby with another MacBook, then you may be able to borrow some charge and keep your laptop alive longer.
Works With Some USB-C Models
MacBook to MacBook charging should work in some capacity on most MacBook models that use USB-C charging. Apple has used USB-C charging on its MacBooks for many years now, and there are reports that this works on both older Intel models and newer Apple Silicon (M1, M2, and variants) machines.
The way it’s supposed to work is that the first person to plug in (using a quality USB-C to USB-C cable that can handle the necessary power) is the one who receives the charge, while the second MacBook connected will be the one providing the power. Sometimes, though (like when one Mac is on the lock screen, or powering up) things behave erratically and this works in reverse.
Which USB-C port you use shouldn’t matter, but if things aren’t working as expected we found that cycling between ports until the “right” MacBook reports that it is charging was sometimes necessary.
Some Things to Remember
We tested this out with two MacBooks: a 2020 13-inch M1 MacBook Air and a 2021 16-inch M1 Max MacBook Pro. The power demands of these machines are quite different, with the M1 MacBook Air shipping with a 30w power adapter while the M1 Max MacBook Pro comes with a 140w adapter.
The MacBook Pro has far greater power demands than the MacBook Air, but even though this was the case macOS still reported that the Pro was charging via the Air. This doesn’t mean that the Pro is sucking down up to 140w from the Air, and you shouldn’t expect to charge a thirsty laptop this way.
Much of the overhead provided by the 140w charger allows the MacBook Pro to use fast charging, which you won’t be doing while connected to something like a MacBook Air.
When we tried this, macOS occasionally reported that “The battery is not charging” before shifting to charging mode. We didn’t see the battery percentage on the MacBook Pro rise after extended use, but we didn’t see it fall either. Conversely, the battery percentage on the Pro fell much quicker while the Air was charging.
What is likely happening is that the Pro is charging very slowly, or simply discharging much slower than it would be otherwise. This might be useful if you have a small amount of charge left and you want to extend what you have (at the cost of another laptop’s battery.)
When Is This Useful?
This might be useful in situations where you have two MacBooks and a single charger. It works best if the machine being charged consumes far less power than the one that’s connected to a power adapter, but you can still potentially extend your battery life if the roles are reversed.
Make sure to reduce your reliance on wall chargers by making sure you keep your MacBook battery in top condition.