Jetstar Japan power-bank flight policy.

Short answer

Jetstar Japan is tracked from Jetstar's official dangerous-goods page, which explicitly maps GK to Jetstar Japan and lists power-bank requirements: power banks must be in carry-on baggage, each passenger may carry a maximum of two, onboard use and charging are not permitted, power banks should be kept within easy reach during the flight, and damaged or defective lithium batteries and power banks must not be carried. The same page separates lithium batteries carried in devices from spare batteries or power banks and provides lithium-battery watt-hour and approval bands for rechargeable portable electronic devices.