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Hello, I put a new battery in a SP4. While plugged in, the SP4 will turn on, boot, run fine. It shows 16% battery, never more, never less. If I unplug from charger, the surface turns off instantly and does not turn back on until plugged back in. Can someone guide me in what to do here?

@focusedtech either a bad battery or issues with your charging circuitry. Replace the battery with your old one and see if that behavior is now different. If it is identical it’s your circuitry , if it has changed replace the battery once more with a different one. Of course always double check your work for properly seated cables, connections etc.