Battery health test
A worn battery is the most common hidden defect in used laptops — and a new one can cost a big chunk of the purchase price. Windows tells you the truth for free in about a minute.
Generate the built-in battery report Critical
Open Command Prompt as Administrator (Start → type cmd → right-click → "Run as administrator"), then run:
C:\> powercfg /batteryreport /output "C:\battery-report.html"
It saves an HTML report to your C: drive. Open it:
C:\> start C:\battery-report.html
Prefer not to type a path? Just run powercfg /batteryreport — it saves to your user folder and prints the exact location in the window.
Read the two numbers that matter Critical
In the report, find the "Installed batteries" section:
- Design Capacity — what the battery held when new (factory spec).
- Full Charge Capacity — what it can actually hold now.
Battery health % = Full Charge ÷ Design Capacity × 100. Example: 38,000 mWh ÷ 57,000 mWh ≈ 67% health (33% worn).
| Health remaining | Verdict | What to do |
|---|---|---|
| 90–100% | Excellent — barely used | Great sign, pay full fair price |
| 80–90% | Good — normal wear | Perfectly fine for daily use |
| 65–80% | Fair — noticeably aged | Usable; negotiate a discount |
| Below 65% | Poor — short runtime | Budget for a replacement battery |
Also scroll to "Battery capacity history" and "Battery life estimates" — these show the trend over time and the estimated runtime.
Negotiation lever: a battery under ~80% health is a concrete, documented reason to ask for money off. Quote the exact number (e.g. "the report shows 71% health") and the price of a replacement battery for this model — sellers find it hard to argue with their own laptop's report.
On a freshly reset laptop the report may be sparse (little history). The Design vs Full Charge numbers are still accurate — those are read from the battery itself.
Confirm with BatteryInfoView Recommended
Run BatteryInfoView from your USB stick (it's portable — no install). Get it from nirsoft.net. It instantly shows:
- Battery Wear Level — the opposite of health (e.g. 12% wear = 88% health).
- Cycle count — how many full charge cycles it's done. Most batteries are rated for ~300–500 cycles before dropping below 80%.
- Designed vs full-charge capacity, voltage, chemistry and manufacture date.
Safety: if the trackpad/keyboard is bulging or the laptop won't sit flat, the battery may be swollen — a fire risk. Don't buy until it's replaced.
Quick real-world drain check Important
- Unplug the charger and use the laptop normally for a few minutes. The battery % should drop gradually and steadily.
- Watch for a sudden drop (e.g. 80% → 40% in a minute) or a shutdown while there's still charge — both signal a failing cell.
- Plug back in and confirm it shows "plugged in, charging" and the % climbs.
- Optional live rate: in Command Prompt run
powercfg /batteryreportagain after a while to compare, or watch the discharge rate in BatteryInfoView.