The fast method — Battery Settings
Apple menu → System Settings → Battery → Battery Health (or 'Battery Condition' on older macOS). This shows 'Normal' or 'Service Recommended'.
'Normal' means the battery is functioning within Apple's expected range. 'Service Recommended' means capacity has fallen significantly — usually below 80% of original — and replacement is worth considering.
The detailed method — System Information
Apple menu → About This Mac → More Info → System Report → Power (left sidebar). You'll see: Cycle Count, Condition, Maximum Capacity (newer macOS), Full Charge Capacity, and Design Capacity.
Apple rates modern MacBook batteries for 1,000 cycles before dropping below 80% of original capacity. A 3-year-old Mac with 600 cycles and 92% capacity is doing well. A 4-year-old Mac with 1,200 cycles and 72% capacity is overdue for replacement.
What 'Maximum Capacity' actually means
It's the percentage of the original new-from-factory capacity that the battery can currently hold. 100% = brand new. 80% = Apple's design threshold for service recommendation. 60% = you'll notice significantly shorter battery life and may want to replace.
Don't panic at 89%. Don't ignore 71%. The number degrades slowly under normal use and dramatically under heavy thermal stress (Pakistani summer + heavy load).
What macOS doesn't tell you that we check at the workshop
Internal cell impedance: a stiff (high-resistance) cell can show 'Normal' but discharge erratically under load. We measure this with proper equipment.
Swelling: macOS has no swelling sensor. You diagnose visually — does the closed Mac rock on a flat surface? Is the trackpad click harder than before? Both = swelling, urgent service.