posted by Thom Holwerda on Mon 8th Feb 2010 23:55 UTC
IconThe past few weeks or so, there's been a lot of interest in a supposed battery status report bug in Windows 7. After installing Windows 7, some users reported seeing "consider replacing your battery"-warnings in systems that appeared to be operating just fine on Windows XP or Vista. After extensive research, Steven Sinofsky has now explained on the Engineering 7 blog that the fault is not with Windows 7 - it really, really is your battery.

Posts all over the web - blogs, forums, articles - popped up, claiming that Windows 7 incorrectly marked batteries as in need of replacement, or, worse yet, that Windows 7 caused these batteries to fail. Microsoft has been investigating the issue, and they have come to the conclusion that Windows 7 is not at fault - those batteries really need to be replaced.

"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," Sinofsky writes on the Engineering 7 weblog, "In every case we have been able to identify the battery being reported on was in fact in need of recommended replacement."

Microsoft has contacted customers who reported this problem, they went over customer service communications, discussed this issue with PC makers, and analysed telemetry data from Windows 7. "To date all such steps indicate that we do have customers seeing reports of battery health issues and in all cases we have investigated Windows 7 has simply accurately detected a failing battery," Sinofsky writes.

Windows 7 makes use of built-in features of batteries that allow the battery health status to be read. "This is reported in absolute terms as Watt-hours (W-hr) power capacity," Sinofsky explains, "Windows 7 then does a simple calculation to determine a percentage of degradation from the original design capacity. In Windows 7 we set a threshold of 60% degradation and in reading this Windows 7 reports the status to you."

The key point here is this: this functionality was not part of Windows XP or Windows Vista. As such, people who think Windows 7 is causing the batteries to fail have it backwards; the battery was already in need of replacement, but XP nor Vista had the ability to report that to you.

In the blog post, Sinofsky gives detailed insights into the data used to come to the conclusion that Windows 7 is not at fault, and from that data, the conclusion is clear. Sorry folks, it's time to go battery shopping.

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