Glenn Fleishman, Macworld:
In macOS 11.0 Big Sur, Apple added full-blown management and visualization, similar to what appears in iOS and iPadOS. The algorithm generally keeps the laptop charged to about 80 percent of capacity. Charging above 80 percent, and particularly to “full,” can put premature wear on a battery, as lithium-ion batteries run hotter the closer they are to their hardware-derived full charge.
However, one reader noted that their battery was always being charged to 100 percent, and wanted to set it to charge no more than 80 percent as a preventative measure. Owners of new M1-based Apple Silicon laptops have found battery life is so remarkably long that they may feel the same way: why risk wearing out the battery when 80 percent gives them more than a full day off the plug?
When I finally managed to get my M1 MacBook Air down to the point where it hit “charge or die”, I noticed that it only charged up to 80%. Glenn Fleishman’s article laid out the why of this.
Still not clear to me why charging sometimes stops at 80% and sometimes goes all the way to 100%. As Glenn mentions, with this exceptional battery life, 80% is plenty for most days, and an acceptable upper limit if it means an extended lifetime for my battery.