Windows 7 Tip of the Week
Get a Free Power Efficiency Report for Your PC

Tip date: July 17, 2010

Windows 7 includes a full complement of power management features, including low-level improvements to core power management technologies and high level user interfaces like the system notification battery meter icon, Power Options control panel, and a newly simplified set of power management plans. PC makers, too, often raise the stakes with their own improvements to the core Windows power management features. Lenovo, in particular, has been very aggressive and successful in this area.

But the basic problem with power management remains: While a stock Windows 7 PC will startup, shutdown, sleep, and resume quite speedily, applications and drivers you install over time can silently change settings and impact the reliability and performance of your PC's power management capabilities as a result. And it's usually hard to know where to look when you're troubleshooting such a problem.

Windows 7 does have one built-in GUI tool for detecting and correcting power management issues: The new Windows Troubleshooting infrastructure, available via Action Center, can examine your power management profile and find out which settings are not optimally configured. To find this Power troubleshooting wizard, open Action Center, click Troubleshooting, and then search for power in the search box.

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You should run this tool. It's basic, but it can find a few obvious issues. If it doesn't find any issues, or if the changes it makes aren't cutting it, you'll need to pry a bit deeper.

Interestingly, Microsoft provides a command line tool, powercfg.exe, for this very purpose. It first appeared in Windows XP and has soldiered on in subsequent Windows versions, including Windows 7. What's most interesting about powercfg is that it provides a superset of the power management functionality that's available in the Windows 7 UI. That is, it can configure any power management features you can configure in Windows 7, or via Group Policy in managed environments, but it also provides additional unique functionality of its own as well.

I don't know enough about powercfg to provide a full tutorial. But then I don't have to: Microsoft has thoroughly documented this interesting command line utility on its TechNet TechCenter web site. What I'm most concerned with here is the utility's ability to analyze your PC for common energy-efficiency and battery life problems and then generate an HTML report. This report can provide clues about which applications, processes, and drivers are causing power management issues.

Here's how it works.

First, open a command line window with administrative privileges. (Open the Start Menu and type cmd in Start Menu Search. Do not tap Enter. Instead, right-click the cmd link that appears at the top of the Start Menu and choose Run As Administrator in the pop-up menu that appears. Click Yes in the User Account Control dialog that appears next. A command line window will appear.

Then, close all other applications and open windows. For powercfg to work correctly, your PC should not be busy with other tasks.

In the command line window, type the following command, and tap Enter when you're done:

powercfg -energy -output c:\energy_report.html

Powercfg will run for 60 seconds, examining your PC.

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When it's done, powercfg will report back how many errors and warnings it found.

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Navigate to your C: drive to find and open the energy report. A typical report will resemble this figure:

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What you see will of course vary from PC to PC. And if you left applications running, they could skew the results.

On my desktop PC, the Zune network service is preventing the PC from automatically entering sleep. My USB root hub is not entering the Suspend state. There are also a number of warnings related to processor utilization, which is "moderate" on this PC. The report recommends reviewing "processor utilization for individual processes to determine which applications and services contribute the most to total processor utilization." This system had a number of issues. But it's also been in service almost a year without a reinstall, and I routinely test software on this machine, so it's pretty "dirty."

On a very recently reinstalled Lenovo ThinkPad, powercfg also found issues with the USB root hub not entering Suspend. And PCI Express Active-State Power Management (ASPM) was disabled because of a known hardware incompatibility with that particular system.

Each PC also provides a long list of warnings and other pieces of information. It's important not to stress over each item, but having an understanding of what's being communicated does help. One small example: On the ThinkPad, powercfg, in a warning, noted that the 802.11 Radio Power Policy was set to Maximum Performance and was not configured to use low-power mode. Sure enough, diving into Power Options, plan settings, Advanced power settings, and then drilling down to the Wireless Adapter Settings option, I could see that it was set to Maximum Performance ... while plugged in. But when operating on battery power, the wireless radio switches to Medium Power Saving, which seems more reasonable.

Each item in the report will require a similar bit of know-how around where to look to solve the problem, if it is a problem, and return your PC to optimal power management efficiency.

Now if only someone would write a book about Windows 7 troubleshooting...