Battery Converter Adapter Tube Sleeve for a 18650 to 20700 | eBay
Amazon.com: 18650 to 21700 and 20700 Adaptor Battery Storage Container(18650 to 21-700 and 20-700 Adaptor) : Musical Instruments
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
18650 Battery Adapter for 2 C-Cells by cohocarl - Thingiverse