Preserve MacBook Battery Life by Limiting Charging to 80%
MacBooks already throttle charging to about 80% when they predict a long plug-in period to protect battery health, a setting you can toggle in Settings > Battery > Battery Health. For more control, you can use the free open-source Battery app to force an 80% cap (or temporarily allow full charging when needed), though you’ll need to plan ahead for times you’ll require a full battery.