Here is the only way to finally solve ES2/ES4 external battery connector issues once and for all. : r/ninebot
Ninebot External Battery Pack extended Battery by Segway Electric Scooter
Buy ES-Series External Battery Mounting Bracket for The Segway Ninebot ES1 ES2 ES3 ES4 Kickscooter - Also Available - Throttle Brake Grips Fenders Online in Hong Kong. B08KHM64J4
Ninebot ES Series, E22 Series, E45 Series Second Battery Pack