Lithium metal batteries deliver extremely high densities of energy, and if they are mishandled they can catch fire, a fire that can't be extinguished with halon, the most common kind of fire-suppression systems in passenger aircraft. That's one reason the FAA banned shipments of nonrechargeable lithium metal batteries on passenger planes in 2004. But that ban only applies in the United States; international authorities are still considering whether to enact such a rule. Cargo and passenger aircraft are free to carry lithium ion batteries, although they are subject to labeling and packing regulations.