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The battery could be bad. The Battery Management circuit could be damaged. I see this a lot in water damaged machines.
Check the voltage at the battery terminals with the power attached. Then check the battery plug with the battery unplugged. If it's dead there is your issue.
There is a fuse on the battery management board "requires you tear into the battery" that has ultra low melting point solder in it. I have seen these fail. I harvest these fuses for the solder and use it at chipquik.
If you have verified that the battery is good check the BMIC lines. In my experience it is usually the battery it's self.
Change U7100.
Be sure battery connector is good and no corrosion under it; you may need to remove and clean/change it.
If still the same, change SMC...