If you have installed the preview version of Windows 8.1 on your Surface RT tablet, you have to expect some bugs pop up. As it turns out, an issue related to a large battery drain on the tablet has been solved by Microsoft via an unusual workaround.
The Microsoft Support forums has a thread from a person who said his Surface RT was experiencing a battery drain at a rate of between two to three percent an hour in Connected Standby mode with the preview version of Windows 8.1 in place. He then posted that a driver called Microsoft UART V2 Driver (\_SB.UAR3) seemed to be the biggest use of the tablet's battery when he used the Powercfg /sleepstudy command.
The response from a Microsoft support member was for the person to turn his tablet's Bluetooth wireless radio on, even though on the surface (no pun intended) that might use even more battery power. The man did as the support person suggested and, lo and behold, the battery drain issue was fixed.
But why did this happen? The Microsoft support team member explained:
Powercfg /sleepstudy reports any issues that are preventing the CPU from entering its lowest power state during Connected Standby (e.g. screen is off). In this case, the state of the specific UART controller is preventing the CPU entering its lowest power state. This UART happens to be connected to the Bluetooth radio on Surface. Unfortunately, the bug that causes this bad state occurs exactly when the Bluetooth radio is turned off in PC Settings.
The support member said this was a known issue with Windows 8.1 on the Surface RT. It's likely this problem will be fixed before Windows 8.1 enters the RTM stage later this month.