For roughly a year and a half, I owned a 2017 NIU N1S. Originally purchased second-hand in Germany, I later imported it to the UK, which is where the projects below took place. The scooter was eventually parted out, but the drivetrain lives in my Vespa LX 50.
This video shows how to replace all of the body panels on an NIU N-Series scooter. While this was done on my N1S (later renamed NQi Sport), the process is more or less the same for the NGT and GTS.
This is an excerpt from the body panel video focussed on the removal and replacement of the ECU.
This video shows how to replace the BMS in an NIU N-Series battery.