How to check your laptop's battery health
Battery wear is the most common reason a laptop's offer changes after testing, and it is almost always because somebody guessed. A battery that feels fine to its owner can measure well below what they expected, especially on a laptop that has spent three years plugged in at a desk.
The calculator asks about it because a worn battery is a cost to whoever owns the laptop next. Checking takes a couple of minutes on any laptop, and gives you a real figure instead of an impression. Macs show it directly. Windows hides it in a report, and this guide shows how to read that report and turn it into a percentage.
Mac: System Settings
- Open the Apple menu and choose System Settings.
- Choose Battery in the left-hand menu.
- Click the information button (the small i) beside Battery Health.
Look for: A Maximum Capacity figure such as 88%, and a status of Normal or Service Recommended. Maximum Capacity is the number to give the calculator.
Mac: cycle count
- Hold the Option key and click the Apple menu.
- Choose System Information.
- Under Hardware in the left-hand list, choose Power.
- Read Cycle Count under Health Information.
Look for: A line such as Cycle Count: 312. One cycle is one full battery's worth of use, spread over any number of charges. A low count with a high capacity is the best combination to describe.
Windows: the battery report
- Right-click the Start button and choose Terminal, Windows PowerShell or Command Prompt.
- Type powercfg /batteryreport and press Enter.
- Windows replies with the location where it saved the report, usually C:\Users\yourname\battery-report.html.
- Open that file in File Explorer. It opens in your web browser.
- Scroll to the section called Installed batteries.
Look for: Two lines: Design Capacity, for example 52,600 mWh, and Full Charge Capacity, for example 44,710 mWh. Design is what the battery held when new. Full Charge is what it holds today. The report also shows Cycle Count on most laptops.
Windows: manufacturer apps
- On a Lenovo, open Lenovo Vantage and look under Device, then Power or Battery.
- On an HP, open HP Support Assistant and run the Battery check.
- On a Dell, open Dell Power Manager, Dell Optimizer or SupportAssist, depending on the model, and look at battery information.
Look for: A health rating such as Good, Fair or Replace, and on some models a capacity figure. These are useful as a second opinion, but the Windows battery report gives the exact numbers.
How to work out the percentage
Divide Full Charge Capacity by Design Capacity and multiply by 100. Using the example above, 44,710 mWh divided by 52,600 mWh is 0.85, which is 85% battery health. That figure means the battery holds 85% of what it held when it was new.
mWh stands for milliwatt-hours, a measure of how much energy the battery stores. You do not need to understand it, only to divide one number by the other. Use the figures from the same report, and ignore the Recent usage section, which describes charging sessions rather than wear.
Occasionally the Full Charge Capacity is higher than Design Capacity on a new battery, or shows a strange value after a battery replacement. If the result is over 100% or looks wrong, tell us what the report says and we will read it with you.
- Design Capacity
- 52,600 mWh
- Full Charge Capacity
- 44,710 mWh
- 44,710 / 52,600 x 100
- 85% battery health