Win7: Checking Battery Health

For years, laptop users who wanted to check the overall health of their laptop battery in Windows had to hope that their OEM included some kind of monitoring software on the OS install, or had to track down a utility from the third-party vendor.

Happily, Windows 7 has a built-in way to check the overall health of your laptop’s battery. It’s not very elegant, and it’s kind of hidden, but it’s a way to know how well your battery is doing:

1) Fully charge your laptop’s battery. It doesn’t matter if you do the remaining steps with the laptop on AC or battery.

2) Click on the “Start” button and type “cmd” (without quotes) in the “Search programs and files” box.

3) Right click on the “cmd.exe” icon in the Start Menu and choose “Run as administrator”.

4) At the command prompt, type “cd %userprofile%/Desktop” (without quotes) and press the ENTER key. Note that the next step will create a report as an HTML file on the desktop; if you want the report in a different location, change to that location instead of the desktop.

5) At the command-prompt, type “powercfg -energy” and press the ENTER key.

The command-prompt will say “Enabling tracing for 60 seconds” and then “Observing system behavior”. After a minute or two, the process will complete and you’ll see a file named “energy-report.html” on your desktop (or wherever you decided to save the file). You may exit the command prompt by typing EXIT and pressing the ENTER key.

Open the “energy-report.html” in your favorite web browser, and scroll towards the bottom of the report. Look for a section called “Battery Information”:

See the two entries called “Design Capacity” and “Last Full Charge”? This tells us how much capacity the battery was designed to have, and how much it actually reported the last time it was charged. I don’t know exactly what units the report measures, but if you divide the “Last Full Charge” by “Design Capacity”, you’ll get the overall percentage your battery is charging to. In the screen cap above, you can see that the battery on my netbook is around 92% (44820 / 48840 = .9176), so that’s pretty good. Once that number gets below 50%, it’s time to replace the battery.