The following update will be listed as “System Firmware Update – 9/15/2015” or “System Hardware Update – 9/15/2015” when you view your update history. USB 3.0 Card Reader driver update (v10.0.10240.31217) improves the system power usage when an SD card is inserted.
Before you go ahead with the update Microsoft warns:
Firmware updates cannot be uninstalled or reverted to an earlier version.
Any update that addresses power usage on the Surface Pro 3 is welcome. Though it remains to be seen if this will help. And by how much.