TLDR
1. Go to > System Settings > General > About > System Report… > Power
2. Check Cycle Count, Condition, and Maximum Capacity.
3. Service/Replace Soon or Max Capacity < 80% usually means the battery is due for replacement.
4. Battery health impacts trade‑in value. Honest, accurate info means a faster quote & payout at SellMac.com.
Example from our screenshots: MacBook Pro (16‑inch, 2021) on macOS Sequoia 15.5 with Cycle Count: 329, Condition: Normal, Maximum Capacity: 82% → Healthy enough to use, but below average for that cycle count; expect shorter runtime. Consider replacement if it dips under 80%.