Amazon.com : PNGKNYOCN 8.4V Battery Pack Housing, with DC and USB Ports Waterproof and Safe Battery Pack Housing, Suitable for 2/4 x 18650 Rechargeable Lithium-ion Battery Bicycle Lamp Headlights and Mobile Phones :
Moli Rocket P42A - 52v 8.4ah eBike Battery | Bicycle Motor Works