Charging an M3 MacBook Air

Just (I hope) to confirm my understanding:

A new M3 MacBook Air can also be charged without harm (however inefficiently) with any USB-C cable connected to any charger?

Not any charger. If the charger has too low a wattage the MacBook Air won’t charge at all, and might not even maintain its existing battery level. If the charger isn’t designed properly then it could fry the charger. I don’t know the minimum rating necessary for a MacBook Air, but I can’t imagine it will be less than 35W which rules out phone and many iPad chargers. However you’re right that it won’t harm the MacBook Air.

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It comes with a 30 watt single charger or 35 watt dual charger, and that’s what Apple recommends using, so I’d say 30 is the minimum. I’ve used the 35 while charging another device and the MBA charges fine.

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My wife has been able to charge her M1 MBA off a 20W charger we originally bought for an iPhone 12. It won’t charge during use, but she closed the lid and had it sleep around ~15% and when she woke it again later in the day it was 100%. Not saying it’s a great idea (who likes super slow charging?), but just pointing out there does not seem to be some special minimum below which nothing at all will happen.

I think the best advice is to just get a quality charger so you know you won’t burn down the house. Sometimes people worry about getting too high wattage chargers, but there’s no risk there (apart from wasting money perhaps). The Mac always decides how many Amps to draw. And frayed cables are something you’d want to avoid. Other than that, enjoy and don’t worry, just let macOS do its thing.

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Two quick points:

You should verify this but if I recall correctly, all Apple devices manage charging automatically (in other words, if a charger is capable of providing “excess” power, the device will only draw the amount of power it is rated for). So, for example, somebody planning to travel with a MacBook Pro and an iPad Mini only needs to carry the MBP’s charger and, of course, each device’s charging cable.

Apple or well-established accessory maker chargers are usually worth the higher cost. Why? Well, I can’t say it any better than this person:

Thanks, all!

Yep…the charging on USB C chargeable Apple devices is handled and managed by the device. So…plugging it into a charger that has a capacity more than it wants it will limit the charging rate appropriately. With a smaller capacity charger it depends on how small. The smaller one may power the device but not charge it or may power and either charge or discharge slowly and will charge faster if the device is asleep than awake and being used.

I charge an M2 Macbook Air using a USB-c cable from an LG 32" display. This also provides video to the display and connects the MBA to an external hard disk attached to the display. All via one cable.
I rarely use the Magsafe cable and power adapter that came with the MBA.