Yes, you can travel by plane with the NeXus Power pack (belonging to the NeXus-10 MKII) without problems. The official guidelines of the International Air Transport Association (IATA) allow you to take it with you. It might differ for each airline how they apply these rules in practice. We recommend to always inquire with the airline before booking a flight.
Please check the official documents of the IATA online to find the guidelines that currently apply:
The capacity of the NeXus-10 MKII Power pack is 29,6 Wh.