Here is the only way to finally solve ES2/ES4 external battery connector issues once and for all. : r/ninebot
Eu Stock Original Ninebot Upgrade Extra Battery For Es1 Es2 Es4 E22 E22e E22d Kickscooter Skateboard External 187wh Battery Kits - Electric Bicycle Battery - AliExpress
Segway-Ninebot External Battery Pack for ES1/ES2/ES4 Electric Kick Scooters : Sports & Outdoors - Amazon.com
Amazon.com : Segway-Ninebot External Battery Pack for ES1/ES2/ES4 Electric Kick Scooters : Sports & Outdoors
Original Ninebot External Battery Mounting Bracket Holder Support Hardware Parts Compatible For Ninbot Es2 Es4 Elecrtic Scooter - Scooter Parts & Accessories - AliExpress