The U.S. Department of Transportation has determined that lithium batteries are a potential fire hazard, and as a result, as of January 1, airline passengers are no longer allowed to pack loose lithium batteries in checked luggage.
Most lithium batteries will be allowed on board when installed in electronic devices. Spare batteries can be placed in carry-on bags if they’re packed properly. However, it’s not as simple as that. All lithium metal batteries (versus lithium-ion batteries) that have more than 2 grams of lithium are forbidden. And lithium quantity limits apply to both your spare and installed batteries.
A chart of what lithium batteries are permitted in checked baggage and in carry-on baggage, as well as information on how to safely pack spare batteries, can be found on the DOT Web site.