MacBook Air battery not charging when shut down

This is the first I've heard of this sort of thing! Does it matter if Mac is left closed or open? That would indicate a flaky connection.

Have you tried starting up in Safe Mode? This bypasses certain potentially disruptive processes, and it often helps. Safe Mode is different for different computers, so see this: 

           Start up your Mac in safe mode - Apple Support 

Here is an article from Apple on some other startup key combinations.

Mac startup key combinations - Apple Support (GU)

This is an Intel based Mac, right? The above includes a link about resetting PRAM on Intel based Macs:

Option-Command-P-R: Reset NVRAM or PRAM.

This is one of those things that sometimes produces magic results. Before you do that, you should look at this article from MacWorld on resetting PRAM, etc.

https://www.macworld.com/article/224955/how-to-reset-a-macs-nvram-pram-and-smc.html

Honestly, I don't hold much hope-- it could be hardware, and I bet your MacAir is really too old for repair to make sense. But it could be software, with a sensor being misread, and one of the above things might fix it. Fingers crossed

🤞

You're running Big Sur on your Mac Air? The most recent update seems to be macOS 11.7.11.

What does your System Settings say about the state of your battery? My M1 MacAir says 82%. Less than 80% is cause for service.

The "smart" systems in Mac power management stop charging when the charge reaches 100%. That would be normal.

Does yours stop charging before reaching fully charged? Does your OS version have a charge-limit setting? In Tahoe:

That's great! Safe Mode is always the first thing to try! It may indicate that you have some 3rd party apps that are causing interference. You should check Login Items in System Settings. The ideal number of login items is 0.

VPNs, "Cleaner" apps, "Virus catcher" apps, and any apps that get system-wide access can cause real problems, and most of us avoid these at all costs. Safe Mode bypasses loading most of these for that reason.