Ever wonder why that advertised "8 hour battery life" never equals more than 4 hours in real life? According to Advanced Micro Devices, the problem with most battery life claims stems from the wide use of a test called MobileMark 2007. Patrick Moorhead, a vice president for marketing at A.M.D., said the parameters for this test include having the screen at just 20 percent brightness, Wi-Fi turned off and no music, video, games or Web pages running. More or less, the test turns a computer into a dimly lit clock, then sees how long it can run.

The reliance on the rather limited MobileMark2007 test proves troubling for a couple of reasons. For one, people really put their laptops through their multitasking paces these days, watching video while puttering around the Web and chatting on the side. It would help to have a test that reflects this behavior. Secondly, we've entered the era of “all-day battery” claims in laptops. Computer makers think customers will pay different prices for computers that last four hours, eight hours, 16 hours and more. Those customers could use a more detailed and accurate measure to figure out if the extra bucks are worth it.