18650 and 21700 vape batteries differ primarily in physical size, capacity, and power output, meaning they are not directly interchangeable unless your vape mod includes a specific adapter.18650 Battery

Dimensions 18mm diameter x 65mm length

Typical Capacity 2,000mAh to 3,000mAh

Device Power Best for standard/dual-battery mods

21700 Battery

Dimensions 21mm diameter x 70mm length

Typical Capacity 3,000mAh to 5,000mAh

Device Power Best for high-wattage sub-ohm mods