Which power banks are allowed on the plane?
Power banks up to 27,000mAh: carry-on luggage
The IATA, an international aviation organization, has established clear rules for flying with power banks. You can take 2 power banks with you. Together, they can have a capacity of up to 27,000mAh. Make sure you put those power banks in your carry-on luggage. They're not allowed as checked luggage. Don't put your power banks at the bottom of your bag, but somewhere you can easily access them. At the security check, you sometimes have to show your power bank.
Larger power banks: differs per airline
The rules for power banks with more capacity than 27,000mAh differ per airline. Power banks with a capacity of more than 43,000mAh can't go with you on the plane. Sometimes, power banks with a capacity between 27,000mAh and 43,000mAh may be taken onto a plane, but only in consultation with the airline. At KLM, for example, you must contact the KLM Contact Center, but the rules are different again for Transavia and Easyjet. Before your trip, check what your airline says about this.
Convert mAh to Wh
If you search the internet for information about power banks and airplanes, you'll most likely come across the term Wh (watt-hours). This is the official, international unit to express the capacity of batteries. You can easily convert mAh (milliampere-hours) to Wh. To do this, you multiply the capacity in mAh by 3.7 and divide everything by 1000. A 10,000mAh power bank has a capacity of (10,000x3.7)/1000 = 37Wh.