As a general rule, power banks can only be carried in cabin baggage, because any rare malfunction in a lithium-ion battery can be responded to far faster in the cabin than in the cargo hold.
Capacity limits are calculated in watt-hours (Wh) and generally fall into three tiers: under 100Wh is unrestricted, 100-160Wh usually requires airline approval and is often capped at two units, and anything above 160Wh is banned by the vast majority of airlines.
Some airlines also cap the total number of power banks a single passenger can carry, commonly set at two, though this can vary on certain international routes, so checking the specific airline's current policy before flying is the safest move.
Having the Wh or mAh and voltage clearly printed on the power bank resolves most questions quickly at security; products with worn-off or unclear labels risk being confiscated by airport staff.
Charjett's power bank products clearly state capacity and voltage information, which makes it easy to both verify airline compliance and pass through security checks without issues.