We are aware of a battery issue that is affecting a limited number of Surface Pro 3 users. We can confirm that the issue affecting these customers was not caused by the software updates issued on August 29th. Our team is actively looking in to the issue to determine the cause and identify a fix. We will post an update as soon as we have more information to share.
Last month, after numerous complaints by a number of Surface Pro 3 users, Microsoft issued a firmware fix meant to help those suffering from extreme battery-drainage issues in models of that device using Simplo batteries.
After that fix, an increasing number of users with LGC-LGC batteries in their Surface Pro 3 devices began reporting they also were noticing battery degradation. Because some began noticing these issues after the Aug. 29 firmware update meant to fix the problems of Surface Pro 3 users with Simplo batteries, some assumed it was that firmware fix that caused the newest round of battery problems.
As the official response above indicates, the company does not believe the firmware update is the culprit, however.
When more information and -- hopefully soon -- another battery fix is available from Microsoft, I'll update this post.