Microsoft's investigation of reports about errant Windows 7 battery messages has shown that the warnings are actually accurate, according to a blog post this afternoon by Steven Sinofsky, the Windows president. Sinofsky's post also explains why the alerts surprised some users: The messages result from a new feature in Windows 7 that alerts users when their batteries are performing at 40 percent or less of designed capacity.

"Essentially the battery was degrading but it was not evident to the customer until Windows 7 made this information available," Sinofsky writes in the post. "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."

In other words, someone who upgraded their machine to Windows 7 from Windows Vista or Windows XP wouldn't have previously seen the alert. The Windows chief gives extensive background and context, and his full post is worth reading, particularly if this is an alert that you've been seeing on your own machine. An excerpt:

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.

The battery issue had initially appeared to be a bump in the Windows 7 launch process, which has overall been considerably more smooth than Windows Vista's debut three years ago.