Here is the only way to finally solve ES2/ES4 external battery connector issues once and for all. : r/ninebot
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Ninebot ES Series, E22 Series, E45 Series Second Battery Pack
Original Segway Ninebot External Battery for ES1 ES2 ES4 & Mounting Bracket 841450007429 | eBay
Ninebot External Battery Kit for ES2 / ES4 Kickscooter
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