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I have a dead Surface Pro3, presumably with a defective battery pack. After many months of looking at it I took the plunge, broke through the screen and have the battery tail with its connector free. The main connector tabs show zero volts but Im not sure if this indicated a dead cell or that I am not enabling a switch within the battery management scheme which is part of the battery pack. Can anyone tell me if the battery tail should be at 7.5V standalone, ie how do I test the battery pack before trying to replace it?

In Windows 10 you can open a command prompt with admin priv and type powercfg /batteryreport /output “C:\battery_report.html

no directly replace it, without doing any test, as you already said the battery is dead so there is no reason to test it, a dead battery could also harm your surface pc , so be cautious.