Can I Bring Fuel Cells Used to Power Portable Electronic Devices and Spare Fuel Cell Cartridges (Flammable Gases or Water-Reactive Material) on a Plane to United States?

According to TSA guidelines, two spare fuel cell cartridges may be carried in carry-on baggage only. Each fuel cell must be marked by the manufacturer "Approved for carriage in aircraft cabin only". Each fuel cell cartridge (not the electronic device) must be marked with the maximum quantity and type of fuel in the cartridge. Though allowed in both carry-on and checked baggage according to international regulations, spare fuel cell cartridges containing flammable gases and water reactive substances are only allowed in carry-on baggage by U.S. regulations.  See FAA Regulations for more information.