Improve Battery Life

Priorities shift when you're not tethered to an AC outlet. Suddenly, processor speed and the glitzy Glass interface just aren't that important when your laptop battery is going to die in 12 minutes. Now, there are things you can do to reduce your laptop's hunger for power, but the best power-saving features are the ones that engage automatically when you're using the battery, but revert to their high-performance settings whenever you plug in.

Start with the obvious: the Power Options page in Control Panel. Here, you'll find at least three plans: Balanced (the default), High performance, and Power saver (which may be hidden under the Show additional plans label). It doesn't really matter which one you choose, because each can be configured any way you like.

Click the Change plan settings link next to the currently selected plan and then click the Change advanced power settings link to open the Advanced Settings window. If it's there, click the Change settings that are currently unavailable link to get rid of this last step.

The settings here that will have the most bearing on your battery life are:

Hard disk

Being a mechanical device, your hard disk eats up a lot of power (those with solid-state devices have my permission to rejoice at this point). Set the Turn off hard disk after option too low, and you'll spend a lot of time waiting for Windows to wake up your hard disk; set it too high, and you're just wasting power. A setting of 10 or 20 minutes is usually a good compromise.

Processor power management

Your processor uses a lot more power than you think. Since it can run at different speeds, it runs fast when needed, but drops down to a slower speed when your PC is idle to save power. The two settings here let you choose the upper and lower bounds of your processor's speed. Unlike with your hard disk, you never have to wait for your processor to be woken up, so there's very little to lose by keeping the Minimum processor state setting as low as possible.

It's worth noting that the Maximum processor state is set to only 50% in the Power saver plan by default; this means that when this plan is active, your CPU will never run faster than about half its rated speed. Of course, this does save power, but as long as the Minimum processor state is set to, say, 5%, it probably doesn't make much sense to limit your CPU in this way. Of course, processors vary, so experiment with this setting to see how well yours manages its own power consumption.

It's also worth noting the System cooling policy, which lets you choose what happens when your processor overheats. Set this to Passive to slow your processor before increasing fan speed; both a slower CPU and a slower fan will prolong your battery. On AC power, choose Active to prioritize speed and activate the fan before slowing the processor to keep things cool.

Display

Use the Turn off display after setting as a battery-friendly alternative to a screensaver. Since it takes very little time to wake up modern laptop displays, set this to a small value like 5 minutes. Next, if your screen has an ambient light sensor, turn on the Enable adaptive brightness option to have Windows automatically adjust your screens brightness as needed. (If you know your screen is equipped with a light sensor and you don't see this option, try updating your monitor driver.)

This setting isn't just for laptops. Microsoft reports that as much as 43% of the total power consumed by a desktop PC is used for the monitor (and that's for a modern, power-sipping LCD display). Choosing an appropriately small value for Turn off display after can save you money and help the environment.

Multimedia settings

In the Multimedia settings branch, the When playing video setting affects how Windows Media Player renders movies when on battery power. Since this is something you're likely to do, say, while on an airplane, you should select the lowest setting you can get away with and still get acceptable video playback.

Click OK when you're done; the changes take effect immediately.

In Windows Vista, you could also choose how aggressively the search indexing service ran while on battery power. (Indexing causes heavy disk and processor usage.) Although this setting is absent in the Power Options window in Windows 7, it never provided the option to disable indexing entirely, so it was of limited value. Thus you may want to stop the indexing service manually while using a battery to save as much power as possible.

To switch between power plans, click the battery status icon in your notification area (tray) and then click the one you want. Or, press Winkey+X to show the Windows Mobility Center, where you can also choose the plan you want.

Switch plans automatically

On a laptop, you'll see two versions of many settings in the Power Options window: one for running on battery power and one for AC. For instance, you can have Windows hibernate after 20 minutes of inactivity on battery, or after 3 hours when plugged in. But what if you want more control?

Programs like Aerofoil (free from http://www.silentsoftware.co.uk/) and Vista Battery Saver (free, http://www.codeplex.com/vistabattery/) can switch power plans automatically based on the power source, as well as turn off the powerhungry Glass interface when you switch to battery power.

Find out if your power-saving measures are paying off

It's fairly easy to get a quantitative report on how much power your PC is using. That way, you can determine if a particular performance downgrade is getting you any real gains in battery life.

One such tool that will show your battery usage is BatTrack, written by the author of the aforementioned Vista Battery Saver (and also available free at http://tinyurl.com/battrack).

But Windows 7 also has a little-known analysis tool of its own, accessible only from the command prompt. To use the tool, open a Command Prompt window in Administrator mode and then type the following:

powercfg -energy -output %userprofile%\desktop\output.html

The analysis will take 60 seconds (which you can change with the optional - duration switch), after which powercfg will save its report as an HTML file on your desktop. Just double-click output.html to view the report.

Anything in red is an issue that could be wasting power: For instance, you'll find out if any of your USB devices refuse to go to sleep (i.e., "USB Device not Entering Suspend"). Below the red sections are warnings (in yellow), which highlight programs using more than their fair share of CPU cycles (i.e., "Individual process with significant processor utilization"). It's not the friendliest report, but odds are you'll discover something that's causing your PC to use more power than it should.

Disable devices, stop services

Don't need that Ethernet port right now? Not using your DVD drive? Turn 'em off and save some more power.

Open Device Manager, expand the branches to show your "expendable" devices, and then right-click each one and select Properties. Choose the Power Management tab, turn on the Allow the computer to turn off this device to save power option, and click OK. Then, assuming the option was available, right-click the device and select Disable (if the option wasn't available, disabling the device won't save any power).

Next, open the Services window (services.msc), and stop any unnecessary services (don't touch the ones you don't understand). For instance, if you've installed Apple's iTunes on your PC, you'll see at least two related services here: Apple Mobile Device and iPod Service. If you have no plans to connect an iPod for the next few hours, right-click each service and select Stop to give your PC one less thing to do while you're running on precious battery power.

Cooler or hotter to save power

One of the most significant things you can do to increase battery life is to take your laptop off your lap. Put it on a book, magazine, airline tray table, tennis racket, pasta strainer, or any hard-and preferably ventilated-surface. If the bottom of your laptop is allowed to breathe, it won't get so hot, and the fan won't have to work so hard to keep the processor cool. The harder your fan works-and for that matter, the hotter your CPU gets-the more power is drained from your battery.

If your laptop never seems to get that hot, even when it's on your lap, you may be able to experiment with some more lenient cooling settings. Using your PC's BIOS setup page or, optionally, a fan control program like I8kfanGUI (free at http://www.diefer.de/i8kfan/), try increasing the allowed temperature of your CPU by a degree or two, and see what happens. With luck, your fan should come on less often and your battery should last a little longer, all without (hopefully) frying your processor.

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