Grand China Air power-bank flight policy.

Short answer

Grand China Air is tracked from Hainan Airlines / Grand China Air official baggage-restriction guidance hosted on hnair.com. The Chinese baggage-restriction page repeatedly scopes the restrictions to 海南航空、大新华航空 and states that power banks are equivalent to spare lithium batteries, spare batteries and power banks are strictly prohibited in checked baggage and must be carried in hand baggage, spare batteries require short-circuit protection, batteries up to 100 Wh do not require Hainan Airlines / Grand China Air approval, batteries over 100 Wh and not exceeding 160 Wh require Hainan Airlines / Grand China Air approval and are limited to two pieces, power banks over 160 Wh or with unmarked/unverifiable rated energy are prohibited, domestic flights prohibit power banks without clear 3C markings or from recalled models/batches, and inflight power-bank charging/use is prohibited.