Last week, Microsoft said it was investigating issues in Windows 7 that affect batteries on certain notebooks after hundreds of users reported they thought the OS was to blame. Steven Sinofsky, president of the Windows and Windows Live Division, has posted a lengthy response on the Engineering Windows 7 blog. "At this time we have no reason to believe there is any issue related to Windows 7 in this context," Sinofsky writes. Here's his explanation:
Several press articles this past week have drawn attention to blog and forum postings by users claiming Windows 7 is warning them to "consider replacing your battery" in systems which appeared to be operating satisfactorily before upgrading to Windows 7. These articles described posts in the support forums indicating that Windows 7 is not just warning users of failing batteries - as we designed Windows 7 to do this - but also implying Windows 7 is falsely reporting this situation or even worse, causing these batteries to fail. To the very best of the collective ecosystem knowledge, Windows 7 is correctly warning batteries that are in fact failing and Windows 7 is neither incorrectly reporting on battery status nor in any way whatsoever causing batteries to reach this state. In every case we have been able to identify the battery being reported on was in fact in need of recommended replacement.
Sinofsky goes on to explain that PC batteries inherently degrade in their ability to hold a charge and provide power, and ultimately batteries must be replaced to restore an acceptable battery life (batteries usually have a warranty of 12 months). Windows 7 taps into a feature of modern laptop batteries which have circuitry and firmware that can report the overall health of the battery in Watt-hours power capacity. Windows 7 then calculates the percentage of degradation from the original design capacity; the threshold is set at 60 percent degradation, so if the battery is performing at 40 percent of its designed capacity then users will see Windows 7 report that it might be time to change the battery.
Further, he notes that Windows 7's new "Consider replacing your battery" message does not exist in Windows XP and Windows Vista, so many users would probably not have been aware of their batteries degrading. This would also explain why some users were seeing the battery indicator in Windows 7 builds prior to the RTM release while others only saw it in the RTM.
Finally, Sinofsky asks users who believe they are receiving this error because their battery is new or in great shape to contact Microsoft via the TechNet forum, the Microsoft Answers forum, or to visit support.microsoft.com to find how to contact Microsoft assisted support in their region.
Source: ars technica