Microsoft has identified a problem that exists in some Windows XP post-Service Pack 2 portables (both Professional and Home editions) that causes battery power to drain abnormally fast when the unit is disconnected from an AC power source
Nor every portable has the problem, but for those that do (implementations of Pentium-M and Core Duo processors seem to be particularly affected), the problem seems to occur under one of two conditions.
The computer can't enter a deep ACPI idle state. PCs that adhere to the Advanced Configuration and Power Interface (ACPI) standard have five power states, labeled C0 to C4. C0 is the standard operating state, while C3 is the deepest sleep state that the computer can be in without actually being completely powered off. When the PC can't enter the deeper sleep states during periods of inactivity, battery power gets used up indiscriminately.
The USB host controller cannot turn off. Most portable computers power down their USB host controllers when they're not in use; some of the machines identified with this problem don't properly power down the host controller when devices are removed. They remain on, and drain power idly.
Microsoft has published a http://www.microsoft.com/downloads/details.aspx?familyid=78E80592-3C1D-46BE-99C2-B0DABAAE4370&displaylang=en>post-SP2 hotfixto address this problem.
Note: There's a third possible cause for this problem. This is when the USB host controller relies on the periodic scheduler for USB 2.0 devices, which is sometimes used to drive interrupt-driven devices such as mice or keyboards. The hotfix will not address that particular problem (although it shouldn't cause any harm).
About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter, which is devoted to hints, tips, tricks, news and goodies for Windows NT, Windows 2000 and Windows XP users and administrators. He has more than 10 years of Windows experience under his belt, and contributes regularly to SearchWinSystems.com and SearchSQLServer.com.
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