the default operation if you literally NEVER use your Mac on battery is to charge to 80 percent.
Once you use it on battery, it will watch how you continue to use it, compile a new typical usage pattern, and adjust the charge level to be ready to meet your anticipated needs (which now may include occasional battery use). Eventually, long periods of no use on battery will cause it to slowly move back toward the 80 percent levels again.
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Batteries are a wear item, like the soles of your shoes or tires on your car. They wear from discharges, and they also wear from the passage of calendar time, even if not used at all. sooner or later, you WILL have to replace the battery.
The additional wear from fully charged is very small, and Apple Battery Health management on battery lifetime is not zero, but is also very small.
About battery health management in Mac laptops - Apple Support
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