I think most 20000mah -50000mah power banks have now high capacity of poweroutput.Make sure to buy a powerbank, which has high output power (power to charge your mobile).
10kmah powerbank which charges your phone in 1 hour >>> 50kmah powerbank which takes forever .
To complicate things even further, some power banks lowers the output power when multiple devices are connected.
And also useful power from a powerbank is about 60-70% of the mentioned rating.
Good luck finding the right one.
AFAIK 30000 mah or above power banks are banned in airplanes.Going for may be 30000 mah or 50000mah will be much better idea but mind you they can be bit bulky.
Yes. That's correct.AFAIK 30000 mah or above power banks are banned in airplanes.