by Kevin Purdy - Laptop batteries are a cruel tool to put your faith in. They're heavy, expensive, and will, by nature, run out and become less effective over time. Then again, they're how you get work done away from the wall socket, and they can be made, if not perfect, at least better performing.
If you haven't already, get to know Windows and Mac OS X's built-in power management utilities, which are easy to locate by typing "Power" into your Start menu or Spotlight search box, respectively. In both systems, you can customize power schemes for best performance (cranking on Photoshop), balanced (web browsing for a good while), or best battery life (20 percent battery and you must grab your boss' email). You should also set up your own custom power scheme with your preferred screen brightness, screen and hard drive time-outs, and other criteria--you might just be more frugal than you know.
Once you've set up those schemes, you'll want to make them accessible, beyond having to right-click on the power icon on the taskbar and head back into your power management scheme. Create a shortcut on your Windows desktop, and in its Properties, have the shortcut point to powercfg /setactive "Name of your power plan", substituting whatever you named your power plan inside the quotes. With that shortcut set up, you can keep it on your desktop, pin it to your Start menu, or assign a keyboard shortcut to switch it on--maybe Ctrl+Alt+B for your "Battery Saver"?
In Windows 7, you can get a more detailed report on what you could be doing better to save energy. Hit the Start menu, type in cmd, and right-click on the Command Prompt option that appears. Select "Run as Administrator," and at the prompt that appears, type in powercfg-energy. Windows will look at your computer running for about 60 seconds, then generate a report on what's using energy and how. Type in energy-report.html, and Internet Explorer will open up with a full report, detailing how your processor scales (or doesn't), how your hard drive and fans operate, and all the way down to when USB devices suspend themselves.
On both Windows and Mac laptops, the biggest energy hog, hands down, is the screen. If you know you're going to be writing or coding for some time, invert your screen colors (Alt+Left Shift+Print Screen on Windows, Ctrl+Option+Cmd+8 on a Mac) and knock your screen brightness as low as you can, while still being able to read your text. Hit the same keyboard shortcut to kick your screen back into normal, not-scary-Tron-like mode.