Electronic smoking devices are allowed only in carry-on baggage.
Passengers are required to take effective measures for preventing accidental activation of the heating element of the device when transporting the devices. See the FAA regulations for examples of effective measures.
Each lithium ion battery must not exceed a Watt-hour (Wh) rating of 100 Wh; or for lithium metal batteries, a lithium content of 2 grams.
Check with your airline on any limitations on the number of devices that can be carried for personal use by a passenger.