Find out why your Windows 7 power management isn't working

We’re focusing on the Windows 7 version of Powercfg here. Windows XP and Vista have a similar tool, but it is not as useful and the instructions here do not apply. Powercfg is what is known as a command-line tool, so we need to open a Command prompt with administrator privileges. Click Start, then All Programs, then click on Accessories and look for Command Prompt. Right-click on this and choose ‘Run as administrator’, typing in the relevant username and password, if asked. A black command prompt window will open: if the text is too small or large, change it by clicking the top-left corner of the window and choosing Properties. Click the Font tab and choose one of the options in the Size box and click OK.

Sometimes a PC won’t enter Sleep mode simply because the PC (or one of its components) does not support power management. To sleep in Windows 7, the PC must support what is known as ‘S3 sleep’. The technical details aren’t important, but to check this feature, type powercfg -A and press Enter. If the brief report says S3 sleep mode is not supported, that will explain why the PC won’t sleep. In this case, check with the manufacturer whether a Bios upgrade is available for the PC. Very few PCs support other modes that may be listed here, so don’t worry if yours doesn’t.

If the PC supports S3 mode but will not sleep, it could be caused by a program that is preventing Windows from sleeping, or simply a file that is open over a home network. Use the command powercfg -requests to show any program that is preventing Windows from sleeping. In our case, Windows Media Player was open and browsing a shared network music folder. Look carefully at the descriptions and you should be able to see which program is responsible. Close the relevant program(s) and/or files and run powercfg -requests again to see if that has fixed it – each category should now say ‘None’.

If the PC regularly wakes up from Sleep mode at odd hours of the day or night, it could be due to a scheduled request from a program, such as an anti-virus scanner or a backup program. Run the command powercfg -waketimers to see if any programs have created such a request. If so, the ‘expires at’ value shows the time and date it is set for. The program or service responsible will also be shown. To see what caused the PC to wake up, use the command powercfg -lastwake and examine the Wake Source entry – in our case, it was the power button.

Powercfg can create an energy-efficiency report file that shows whether a notebook’s battery is performing correctly or is failing. First, close all running programs and tasks. Create a folder for the report by typing md c:\energy and pressing Enter (no message will appear). Now type powercfg -energy -output c:\energy\energy.html. The program runs for 60 seconds, so don’t turn off the PC or touch the mouse or keyboard until it stops. It will display a short summary of errors and warnings when finished, but we’re not interested in these.

Still in the Command Prompt window, type the full name and location of the file specified in Step 5 (in this example, c:\energy\energy.html), then press Enter. The file will open in the default web browser. Scroll down to near the bottom of the page to the ‘Battery: Battery Information’ section. For a healthy battery, the Last Full Charge figure should be similar to the Design Capacity figure. If it is less than half, the battery life will be poor and the battery itself may be approaching the end of its useful life. If it is a new battery, this could indicate a defect.