Shenzhen Airlines power-bank flight policy.

Short answer

Shenzhen Airlines publishes an official lithium-battery carriage PDF. The notice says power banks are small rechargeable lithium-battery devices used to supply external power to portable electronics and must comply with spare-battery transport requirements: spare batteries are hand-baggage-only, individually protected against short circuit, and limited to 20 per passenger. Lithium-ion spare batteries up to 100 Wh are allowed under the ordinary spare-battery rule, while 100-160 Wh batteries must be declared at check-in and transported only after inspection and approval with a two-piece limit. Power banks may not be used to charge devices onboard, may not be charged onboard, must remain switched off if they have a power switch, and China domestic flights prohibit power banks without 3C marking, unclear 3C marking, or recalled model/batch status.