Microsoft has rolled-out a new firmware update for Surface Pro 3 that fixes the severe Battery issue faced by some owners. Due to this issue some Surface Pro 3 batteries were misreport charging capacity and charging.
The last firmware update of August month brings lot of issues with the battery. So according Microsoft, the battery issue with the Surface pro 3 was due to the firmware ( not due to the hardware).
v126.96.36.199 corrects an error that may occur on a limited number of Surface Pro 3 devices where the full charge capacity of the battery is misreported to the operating system and device firmware. This update corrects the firmware component that functions as a “fuel gauge” so that the battery capacity is accurately reported. See Surface Pro 3 Battery FAQ for more information.
You can get this update by navigating to Settings > Update & security > Windows Update on your device.