News

Microsoft Tells Windows 7 Users To Change Their Batteries

• By Kurt Mackie
• 02/08/2010

Windows 7 users who have received alarming messages about needing to replace their laptop batteries may just be getting better information from their operating system, according to Microsoft's Windows 7 team.

Microsoft addressed the issue on Monday in a new post in the famously long-winded "engineering Windows 7" blog. According to Microsoft, Windows 7 does not alter battery life information. Instead, it takes read-only information from the firmware or BIOS. What's new with Windows 7 is that the operating system now makes an estimate, based on the firmware data, about the probable life of the battery.

"Windows 7 makes use of a feature of modern laptop batteries which have circuitry and firmware that can report to Windows the overall health of the battery," the blog explains. "This is reported in absolute terms as Watt-hours (W-hr) power capacity. 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 (that is the battery is performing at 40% of its designed capacity) and in reading this Windows 7 reports the status to you."

This calculation does not take place in Windows Vista or Windows XP, which do not support this feature, according to the blog. Windows 7 uses the "design capacity" and "last full charge capacity" information in the BIOS to determine the battery's degradation state.

So far, Microsoft has investigated 20 incidents associated with the battery failure message but "none of these have shown anything other than degraded batteries," the blog explained.

So, the mystery of the "consider replacing your battery" message would seem to be solved. These users just have bad batteries! However, that explanation did not appease DanLee81, who initially described the problem back in June on a Microsoft TechNet forum Web page.

In reply to the blog post, DanLee81 stated that Microsoft may be pulling the wrong data from the BIOS. Microsoft should use the "total capacity" variable instead of the "design capacity" variable. This claim led to a clarification from Pat Stemen of Microsoft.

"Total Capacity can not be used for this warning as its value changes quickly at runtime as the battery is charged and discharged," Stemen wrote in the blog. "We call Total Capacity 'Remaining Capacity' and it is the value used to determine the % remaining and in conjunction with the rate of drain, the estimated time remaining."

The blog, signed by "Steven" (perhaps Microsoft Windows Division President Steven Sinofsky), encourages users with new batteries who think they are experiencing this battery-failure message problem to contact Microsoft. The options for getting in touch include using "the TechNet forum, the Microsoft Answers forum, or visit support.microsoft.com, where you can get additional information about how to contact Microsoft assisted support in your region."