What if the airline asks me about the battery?

Since these policies are still new, everyone at the airlines (or in line at security) might not be as up-to-date as you. If an employee ever has a question about your bag (or the rules), you can find the policies of the major US airlines below.

American Airlines

"You can travel with these bags as a carry-on bag. If the bag needs to be checked or valeted you must remove the battery and carry it with you."

From American Airline's policy page as of February 1, 2018.

Delta

"Customers checking a smart bag with a removable lithium-ion battery must remove it and take it with them into the cabin. Customers carrying-on a smart bag containing a removable lithium-ion battery must remove it from the designed enclosure prior to boarding the aircraft. This is consistent with Delta's policy today requiring customers to place spare lithium-ion batteries in their carry-on luggage."

"Pack spare batteries in carry-on baggage."

From Delta Airline's official statement and from their policy page as of February 13, 2018.

United Airlines

"Effective July 9, lithium batteries that are installed in any checked or carry-on baggage must be removed by the customer. Once removed, these batteries can be transported on board."

From United Airline's policy page as of July 9, 2018.