18650 to 20700/21700 Battery Adapter by AnalogDan - Thingiverse
BESTSUN 3.7-4.2V Li-ion AC Charger Wall Charger Adapter with LED Indicatior for 18650 Battery Powered Rechargeable LED Flashlight Torch and Headlamp with Charging Port - - Amazon.com
Lithium Batteries Charging Adapter Universal USB Battery Charger for 4.2V 18650 18490 Li-ion Batteries 1 Slot Black - Walmart.com
Authentic Vandy Vape 18650 Battery Adapter for Pulse BF 80W Box Mod