Passengers can take two loose batteries with them in their carry-on baggage, but only if each battery is in a separate resealable plastic bag or its original packaging.

Common consumer electronics such as travel cameras, cell phones and most laptop computers are still allowed in both carry-on and checked luggage with their lithium batteries inside them.

Lithium batteries are considered hazardous materials because they can overheat and ignite in certain conditions, the Department of Transportation said.

Safety testing conducted  by the FAA found that current aircraft cargo fire suppression system would not be capable of suppressing a fire if a shipment of not-rechargeable lithium batteries were ignited in flight, it said.

"Doing something as simple as keeping a spare battery in its original retail packaging or a plastic zip-lock bag will prevent unintentional short-circuiting and fires," said Krista Edwards, deputy administrator of the DOT's Pipeline and  Hazardous Materials Safety Administration, in a press release issued last week.