When should I replace my MacBook Air battery?

Regarding the MacBook Air: Replace it when you notice swelling (clicky trackpad, bulging case), fast draining (charging twice daily for light use), shutdowns at 20%, or “Service Recommended” in the battery menu. Apple says 1000 cycles is the limit, but start thinking about a swap past 500 cycles if you see degradation. Don’t wait — a weak battery can also slow down your CPU. Stick with Apple for the replacement ($130–$200) rather than third-party batteries.