Surface Pro 4 battery charge capacity negative; Surface only stays on

there could be two reason:-

1. Battery itself has started malfunctioning as surfacepro 4 batteries available in market are not upto that standard and stop working. its not easy to get a right battery for surfacepro 4. I have gone through this problem. replaced 100s of batteries in surface devices but always had problem with pro4 batteries.
2. Motherboard issue- While replacing battery a isolating diode (that isolate adapter power and battery power and power up the device in absence of adapter) gets burnt out most of the time. then device stopped recognizing the battery. Need to replace the diode in this case.

better to contact a person who know more about surface devices.

Hi Oana.

I had exactly the same symptoms (255%...) after changing my old swollen battery with a "new" one bought from ifixit. Furthermore, my surface pro 4 tablet only worked with the charger connected.

I tested by disconnecting the battery from the motherboard with a small piece of cardboard to make sure my tablet still booted, which it did.

Then, thanks to the powercfg system command report, it turned out that the "new" battery was over 5 years old and had undergone numerous charge/discharge operations.

I also found on other forums that the indication -1 mWh meant a dead battery.

Ifixit reimbursed me for it and I bought another one on Amazon which allows me to use the tablet autonomously again.