Laptop Battery Health Explained: Capacity, Cycles, and When to Worry

Design capacity vs full-charge capacity

Every battery ships with a design capacity (what it could hold when new) and develops a lower full-charge capacity as it ages. Battery health is simply the ratio between the two. A battery at 45 Wh full-charge against a 50 Wh design is at 90% health.

• 90-100%: excellent — effectively new.
• 80-90%: good — normal for a lightly used machine.
• 60-80%: usable — expect noticeably shorter runtime.
• Below 60%: plan for a replacement battery.

Cycle counts

One cycle is one full discharge-and-recharge (which can span several partial charges). Most modern laptop batteries are rated for 500-1000 cycles before dropping to ~80% health. A three-year-old laptop with 200 cycles has plenty of life left; one with 900 is near the end of its original battery.

How to check it yourself

On Windows, open Command Prompt and run powercfg /batteryreport — the generated HTML report shows design capacity, full-charge capacity, and usage history. On a Mac, hold Option and click the Apple menu → System Information → Power for cycle count and condition.

RouteCheck's diagnostic suite reads the same data directly from the battery controller during testing, so a certified device's report already includes real measured health — not a seller's estimate.

When it's a dealbreaker

For a machine you'll use on the move, don't accept below ~75% health unless the price reflects a battery replacement (typically £40-120 depending on model). For a desk-bound laptop that lives on the charger, battery health matters far less — knock it down your priority list and negotiate instead.