Waterproof Case 21700 - Battery Storage Boxes - AliExpress
HΩ RUN – 21700 (2 pack)
21700 Cylinder Cell Case with Anti-Explosive Cap and Insulation O-ring - 100 Pcs/package - EQ-Lib-18650-1
Fenix 21700 Rechargeable Li-ion Battery - 5000 mAh - V2 – Fenix Store
Amazon.com: JJC Battery Pouch Case for 4 x 18650, 20700 or 21700 Battery, Belt Holster for 18650 Battery with Carabiner, Zipper Pocket Memory Card Storage : Sports & Outdoors