Ninebot Max Error Code 39
"Internal Battery Temperature Sensor is abnormal. Please replace the Battery."
This error is caused by the battery temperature sensor reporting a value outside the expected range.
This may be because it is too hot or cold, or may be triggered for no reason.
Check the temperature of the battery in the app. If the temperature is abnormally hot, let the battery/scooter cool down a bit.
If the temperature is abnormally cold, take your scooter out of the cold and let it warm up.
If the temperature does not appear abnormal, just restart the scooter.
This has happened to me a number of times where I am braking and the error appears despite the battery being roughly room temperature.
If the issue persists frequently, it may be worth flashing custom firmware to ignore battery errors.