Airplane Regulations
In the current version of the fin, the battery is not removable, but shouldn't cause any issues with the airplane regulations. You can have it in the carry-on with you as it fits the limits of 100wh (learn more here Boost Fin Specs).
Lithium batteries with more than 100 watt-hours may be allowed in carry-on bags with airline approval. One spare battery, not exceeding 300 watt-hours, or two spare batteries, not exceeding 160 watt-hours each, are permitted in carry-on bags.
Tip: Be sure to take out the screwdriver if you plan to travel with your Boost Fin in a carry-on bag. It's recommended to put the screwdriver in the baggage.