MacBook Air M4: MagSafe light stays amber until startup
Based on the behaviour described, I wouldn’t immediately suspect a hardware fault with your MacBook Air M4, 35 W power adapter, or MagSafe cable.
According to Apple’s guide to charging a MacBook Air, the MagSafe indicator glows amber when charging is underway or on hold, and green when the battery is fully charged.
Since you’ve set an 80% charge limit, your Mac can stop charging before reaching 100%. Apple confirms that macOS may display “Charged to [%] Limit” when the battery reaches its configured limit. However, this alone doesn’t fully explain why the indicator remained amber for several hours and turned green only when you opened the lid and the Mac began booting.
See Apple’s explanation of Charge Limit and Optimized Battery Charging.
The fact that the light changed during startup is encouraging, but it doesn’t conclusively rule out a software or hardware issue. Apple’s documentation explains the indicator colours and charging behaviour, but it doesn’t establish why this particular change occurred during startup.
Recommended checks
Check the battery status
After startup, click the battery icon in the menu bar and check whether macOS reports “Charged to 80% Limit,” “Charging On Hold,” or “Not Charging.”
Apple explains these statuses in its Charge Limit and Optimized Battery Charging guide.
Test charging while the Mac is running
If the battery is below 80%, connect the MagSafe cable and check whether the percentage increases normally. Observe whether the indicator turns amber while charging and green when the battery is fully charged.
Apple’s MacBook Air charging guide explains the expected charging indicators.
Temporarily test a full charge
If you want to check whether the 80% limit is relevant, use the battery menu’s Charge to Full Now option, if available, rather than permanently disabling your charge limit. Observe the indicator as the battery charges.
Apple documents this option in About Optimized Battery Charging and Charge Limit on Mac.
Check the adapter and cable
Ensure all connections are secure and the ports are clean and dry. If possible, test with another compatible Apple power adapter and a suitable charging cable.
A 35 W adapter is not inherently unsuitable: Apple lists its 35 W Dual USB-C Port Compact Power Adapter as an option for the 13-inch and 15-inch MacBook Air. A higher-wattage adapter may provide faster charging in supported configurations, but switching adapters is not necessarily a fix for this indicator behaviour.
See Apple’s MacBook Air charging guide.
My assessment
If the battery charges normally, the indicator remains steady, and no charging warnings appear, I wouldn’t treat this single incident as evidence of a hardware defect.
The 80% limit may explain why charging stopped, but it doesn’t conclusively explain why the light changed colour only when the Mac started up.
If the behaviour recurs, the battery fails to charge when it is below the limit, or the MagSafe indicator repeatedly flashes amber, consult Apple’s troubleshooting guide: If your Mac battery won’t charge. You can also use Apple Diagnostics to help identify possible hardware problems.
Since you mentioned that you’re running macOS 27.0 and the behaviour is new, it’s worth investigating if it persists. I wouldn’t attribute it to that macOS version without further evidence.
In short: there’s no immediate reason to assume that your Mac, adapter, or MagSafe cable is defective.
A repeatable charging test and the battery status reported by macOS should help narrow down the cause before you consider servicing the device.
