According to a problem of a user -Microsoft UART V2 Driver (\_SB.UAR3) seemed to be the greatest consumer of battery when he came to conclusion using Powercfg /sleepstudy command.
And the workaround suggested by Arvind M. [MS]:-
“turn it on as a workaround. Swipe in from right to bring in charms bar, tap on Settings and then on Change PC Settings at the bottom. Subsequent steps to get to the switch to enable Bluetooth:
Change PC Settings
PC and Devices
“Powercfg /sleepstudy reports any issues that are preventing the CPU from entering its lowest power state during Connected Standy (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.
It is reasonable to want to turn off the Bluetooth radio to conserve even more power, but be aware that the major contributor to drain on battery is overall system power use, not just an individual radio.
Microsoft teams are aware of this issue in the preview build of Windows 8.1.”