My XTAR X4 Extended is able to charge an Olight 18650 (not too surprised). However, it is somehow also able to charge the Olight 21700 despite the plastic ring around the positive
Olight 21700 5000 mAh teardown : r/flashlight
Accumulateur li-ion Olight 21700 4000 mAh
Olight Odin Flashlight – Beeyoutiful.com
Rechargeable 21700, 5000mAh 3.6v battery - Olight Store
Olight Perun 2 2500 Lumens Multi-Functional Vertical handheld Flashlight, MCC Rechargeable 21700 Headlamp with Headband (H2R Upgrade) - Walmart.com
Olight ORB-185C20 18500 2040mAh suitable for Odin-mini - AliExpress