Error 21 on Segway-Ninebot E2 Pro

In plain English

The battery has its own management system that watches its cells, temperature and charging. This code means it found a problem. Never open the battery: contact support.

Work from the top. Steps go from free and easy to shop jobs. Switch the scooter off before touching any connector. Tick each step as you go. Your progress is saved on this device.

1. 1Switch off and restartFree Turn the scooter off, wait 30 seconds, then turn it back on. If the code clears, note what you were doing when it appeared, in case it comes back.
2. 2Check the outside of the deck (don't open it)Free Look at the outside only. If the deck is swollen or cracked, the charge port is wet or burnt, or it's very hot or smells, don't ride or charge it and contact support. If it smokes, get everyone out and call 911.
3. 3Write down the code and when it happensFree Take a photo of the display and note when the code appears: at switch-on, when you set off, on hills, in rain or while charging. Support will ask for this.
4. 4Contact support or a service centerShop job If the code stays after these checks, stop riding and contact the brand's customer support or an authorized service center. Don't open the deck, battery, controller or motor: most scooter batteries and controllers aren't user-serviceable.