Apple says that if you have a specific Mac, and are running at least macOS 10.15.5, you should not be concerned if you see “Not Charging” while you’re charging your Mac.
Apple recently launched a dedicated support document for this particular issue (via MacRumors), and it basically boils down to this: things are working as intended, please don’t panic. As one might expect it might be a little alarming to see that your computer is not actually charging even though you have it plugged into power, but the company says this is a feature, not a bug.
The support document states that if you’re running a Mac with Thunderbolt 3 ports and the computer is running at least macOS Catalina 10.15.5, the battery health management feature is the reason behind the “Not Charging” notification. The battery health management feature is designed to prolong the life of the Mac’s battery by “reducing the rate at which it chemically ages”. To that end, the feature will constantly monitor the Mac’s battery temperature history and patterns related to charging.
As for when you might see “Not Charging”, Apple says this:
When battery health management is turned on, you might occasionally see ”Not Charging” in the battery status menu of your Mac, and your battery’s maximum charge level might be lowered temporarily. This is normal, and it’s how battery health management optimizes charging. Your Mac resumes charging to 100 percent depending on your usage.
However, there are some things to be aware of because the “Not Charging” indicator might pop up for another reason, too: not enough power. If you see “Not Charging” while your Mac is plugged in, it might be due to the fact you’re not using the correct cable or power adapter. Make sure you’re connected to a power supply that’s providing enough power, and that may fix the issue, too.
The battery health feature is a nice addition to Mac (and Apple handled the rollout of the feature much better than it did with the iPhone), but these warnings can lead to plenty of confusion. This support document is meant to address that.
Have you seen “Not Charging” on your Mac before?