According to Engadget, the old worry that leaving a MacBook plugged in will damage its battery is largely outdated. Modern MacBooks use lithium batteries and smart charging software that monitors temperature history and charging patterns, pausing charge at optimized times. The battery health management feature is on by default for Macs running Catalina 10.15.5 or later.
Still, the article notes caveats. Heat remains the biggest issue: using a laptop on a warm day or in a case that blocks airflow while charging can shorten battery life. Apple lists MacBook Air operating temperatures as 50° to 95° F, and users should keep fans unblocked if the device gets hot.
Engadget also points to storage behavior. If a MacBook will sit unused for a long period, Apple recommends charging it to around 50 percent; storing it fully charged can cause capacity loss. Checking Battery Health in System Settings shows whether the battery is normal or needs service, with replacement generally suggested below 80 percent capacity.