Rex Airlines power-bank flight policy.

Short answer

Rex Airlines publishes an official Power Banks and Spare Batteries page. The page says power banks must not be used at any time on board a Rex aircraft, power banks and external spare batteries must remain switched off, disconnected, and individually protected, and power banks and external spare batteries must be packed in carry-on baggage only. Each passenger may carry no more than two power banks and 20 spare batteries in total, and any bag containing these items must be placed under the seat or the items removed to the seat pocket rather than stowed in an overhead locker.