Jeju Air power-bank flight policy.

Short answer

Jeju Air publishes official Korean transport-limit guidance for power banks. Power banks are carry-on only and cannot be checked; they must be protected against short circuit and kept on the passenger or in a visible cabin location, not in overhead bins. Jeju Air allows power banks up to 160 Wh with a two-unit limit, prohibits power banks over 160 Wh, requires check-in counter airline approval for 100-160 Wh power banks, and says 100-160 Wh power banks and spare batteries are limited to two combined. Jeju Air prohibits power-bank use and charging during flight, with an exception for needed medical-device use, and bans swollen or damaged lithium batteries.