Q: My MacBook won't turn on when not plugged and battery indicator says battery is unavailable

1. Hold the option key down  and click the battery icon in the menu bar.

    Is  the Condition stated as "Normal"?

2 Reset SMC and test.

      Reset SMC. Choose the method for “On Mac notebooks with non-removable battery”.

      https://support.apple.com/en-us/HT201295

Open System Infoirmation>Power and post this from your MBP:

make certain that the charger is connected.

Run an Apple Hardware Test:

https://support.apple.com/en-us/HT201257

Note that an error free AHT is not conclusive.

Ciao.