Microsoft says that extensive testing and conversations with OEMs indicate that Windows 7 is handling notebook batteries exactly as intended - despite user claims that upgrades to the new OS have caused significant degradation to battery life.

As we reported in late January, various laptop owners - including a string of posters to Microsoft's TechNet forum - have said that after upgrading their laptops to Windows 7, they've seen a decrease in battery life. The claims involve a new Windows 7 tool designed to inform the reader when tlheir battery needs replacing.

According to some users, Windows 7 is displaying the message "Consider replacing your battery" even though their batteries are brand new, and some say that this message pops up in tandem with sudden battery life reductions. But in a Monday post to the Engineering Windows 7 blog, Windows and Windows Live president Steven Sinofsky says the notification tool is operating as designed.

"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," the post reads. "In every case, we have been able to identify the battery being reported on was in fact in need of recommended replacement."

Windows 7 taps into circuitry and firmware in today's laptop batteries that reports power capacity in Watt-hours. The OS then calculates how much this figure has decreased from the capacity provided by the battery's original design specs. If the capacity reading drops below 40 per cent of the original design capacity, Windows 7 notifies the user.

This tool was not available with Windows XP or Vista, and Microsoft says that according to its testing, Windows 7 is simply providing information that previous OSes did not. "It should stand to reason that some customers would be surprised to see this warning after upgrading a PC that was previously operating fine. Essentially the battery was degrading but it was not evident to the customer until Windows 7 made this information available.

"We recognize that this has the appearance of Windows 7 'causing' the change in performance, but in reality all Windows 7 did was report what was already the case."

Some posters said they were seeing significant battery degradation on new batteries, but Microsoft says it has not found any reports where the hardware was in fact new. "We have seen no reproducible reports of this notification on new hardware or newly purchased PCs. While we’ve seen the reports of new PCs receiving this notification, in all cases we have established that the battery was in a degraded state."

That said, Microsoft adds that if you receive Windows 7's battery replacement notification and you believe it's in error, you should contact your PC maker. You can also seek help in the forums at TechNet or Microsoft Answers or by sending the Engineering Windows 7 team an email through the blog's contact form. ®

Update: This story has been corrected to show that Windows 7 notifies the user if it calculates that a battery's capacity reading drops below 40 per cent of the design capacity - not 60 per cent.