Spare lithium-ion batteries, including power banks and charging cases, are never allowed in checked bags and "must be carried in carry-on baggage only," according to the FAA's website. But the agency's rules are fuzzier when it comes to many battery-powered devices passengers travel with. The FAA's PackSafe webpage says passengers "should" pack lithium battery-powered personal electronic devices in carry-on bags, but also states that these devices can be packed in checked luggage as long as they are "completely powered off and protected to prevent unintentional activation or damage," adding "most consumer personal electronic devices containing batteries are allowed in carry-on and checked baggage."
The main risk is that these batteries can overheat and go into thermal runaway, a chain reaction that occurs when a lithium-ion cell enters an uncontrollable, self-heating state -- resulting in extremely high temperature, smoke and, ultimately, a fire that is notoriously difficult to put out. The average passenger brings four devices on a flight -- including smartphones (81%), laptops (40%), wireless headphones (38%) and tablets (35%), according to a 2024 survey of over 12,000 adults by UL Standards & Engagement (ULSE), a nonprofit organization that develops and advocates for safety standards in various sectors, including the airline industry. According to FAA data, 39% of lithium-battery incidents on aircraft reported since 2006 involved portable chargers. The next-biggest culprit was vape pens, responsible for 21% of incidents.