Airlines are taking on a new flight-safety risk: the portable charger.

The lithium-ion battery packs are increasingly popular among travelers looking to keep their phones and other electronics juiced up. But the power banks are also a leading cause of cabin fires, sparking more incidents than any other rechargeable device.

To reduce the growing fire hazard, airlines are adding new precautions on top of banning the batteries from checked luggage.

American Airlines last week prohibited passengers from recharging power banks using in-flight outlets, matching the policies of Delta Air Lines and Southwest Airlines. Southwest also recently limited travelers to one portable charger each.

Some international carriers have taken even stronger steps. Trade leaders, crew unions and aviation officials said they expect more airlines will follow suit.

“If we wanted to make it completely safe, there would be no batteries on airplanes,” said Lynn McGuigan, who leads the cargo safety section at the United Nations’ International Civil Aviation Organization. “But realistically, we know that can’t happen. So we’re dealing with reality.”

The airplane fire threat is a side effect of the proliferation of cellphones, tablets and other electronic devices powered by rechargeable batteries. More travelers are toting portable chargers to keep their digital equipment powered throughout their journeys.

Haley Andringa, who flies cross-country on American twice a month for her makeup artistry business, travels with up to three portable chargers. She works on her flights, and worries most about regional legs and tight connections without reliable in-flight power.

“It’s become such a travel essential,” she said.

All lithium batteries can uncontrollably heat and catch fire through a chemical chain reaction known as thermal runaway. Power banks are especially vulnerable, because unlike cellphones or laptops, they are often made without built-in protection against fires.

Adding to the risk: Many of the power banks are cheaply made or even counterfeit, and passengers handle them with less care than their more expensive electronics, said Jeff Marootian, chief executive of safety firm UL Standards & Engagement.

Power banks sparked more reported airplane fires and thermal runaway incidents than any other lithium-battery device in 2025, said the ICAO. Airlines reported lithium battery events involving fire, smoke, or extreme heat nearly twice a week on average last year, more than double the incidents in 2020, according to Federal Aviation Administration data.

When a battery pack does overheat, flight attendants must move fast. Crews typically cool the device with water and place it in a fire-containment bag to keep the heat and smoke from spreading.

“Keeping devices within reach can mean the difference between a contained incident and a serious event,” said David Wroth, who leads UL Standards & Engagement’s research on thermal runaway incidents.

In March, the ICAO said the products should be within arm’s reach and never charged onboard. The FAA, which said it is considering the organization’s stricter guidance, currently bars the devices from checked luggage and restricts passengers to two portable chargers in carry-on bags.

Airlines’ rules vary, leaving passengers to navigate different restrictions on their portable chargers from one airline to the next.

Delta matches the ICAO specifications, while United Airlines, which bans portable chargers and vapes from overhead bins, hasn’t prohibited power banks from being charged onboard. Meanwhile, Japan’s transport ministry and South Korea’s major airlines have banned passengers from using portable chargers in flight altogether.

Daniel Rodríguez, who commutes between Atlanta and Philadelphia, worries that a lack of compliance with portable-charger restrictions could lead to boarding-gate chaos. “If people don’t follow the rules, does it cause delays? Do we deplane?” he asked.

American and Southwest said they aren’t searching travelers to enforce their newest policies. Instead, the airlines are counting on passenger education, including cabin announcements and questions from gate staff.

Michael Massoni, safety chair for the Transport Workers Union Local 556 representing Southwest flight attendants, said passengers have reacted positively to the safety announcements he has delivered.

“The look that I’m seeing on their faces is not one of pushback or disgust,” Massoni said. “It’s more of, ‘wow, that makes sense.’”

Southwest plans to outfit its entire fleet with in-seat power by the middle of next year so that passengers won’t rely on portable chargers, said Dave Hunt, the airline’s vice president of safety and security.

Write to Amira McKee at amira.mckee@wsj.com

Airlines are taking on a new flight-safety risk: the portable charger.

The lithium-ion battery packs are increasingly popular among travelers looking to keep their phones and other electronics juiced up. But the power banks are also a leading cause of cabin fires, sparking more incidents than any other rechargeable device.

To reduce the growing fire hazard, airlines are adding new precautions on top of banning the batteries from checked luggage.

American Airlines last week prohibited passengers from recharging power banks using in-flight outlets, matching the policies of Delta Air Lines and Southwest Airlines. Southwest also recently limited travelers to one portable charger each.

Some international carriers have taken even stronger steps. Trade leaders, crew unions and aviation officials said they expect more airlines will follow suit.

“If we wanted to make it completely safe, there would be no batteries on airplanes,” said Lynn McGuigan, who leads the cargo safety section at the United Nations’ International Civil Aviation Organization. “But realistically, we know that can’t happen. So we’re dealing with reality.”

The airplane fire threat is a side effect of the proliferation of cellphones, tablets and other electronic devices powered by rechargeable batteries. More travelers are toting portable chargers to keep their digital equipment powered throughout their journeys.

Haley Andringa, who flies cross-country on American twice a month for her makeup artistry business, travels with up to three portable chargers. She works on her flights, and worries most about regional legs and tight connections without reliable in-flight power.

“It’s become such a travel essential,” she said.

All lithium batteries can uncontrollably heat and catch fire through a chemical chain reaction known as thermal runaway. Power banks are especially vulnerable, because unlike cellphones or laptops, they are often made without built-in protection against fires.

Adding to the risk: Many of the power banks are cheaply made or even counterfeit, and passengers handle them with less care than their more expensive electronics, said Jeff Marootian, chief executive of safety firm UL Standards & Engagement.

Power banks sparked more reported airplane fires and thermal runaway incidents than any other lithium-battery device in 2025, said the ICAO. Airlines reported lithium battery events involving fire, smoke, or extreme heat nearly twice a week on average last year, more than double the incidents in 2020, according to Federal Aviation Administration data.

When a battery pack does overheat, flight attendants must move fast. Crews typically cool the device with water and place it in a fire-containment bag to keep the heat and smoke from spreading.

“Keeping devices within reach can mean the difference between a contained incident and a serious event,” said David Wroth, who leads UL Standards & Engagement’s research on thermal runaway incidents.

In March, the ICAO said the products should be within arm’s reach and never charged onboard. The FAA, which said it is considering the organization’s stricter guidance, currently bars the devices from checked luggage and restricts passengers to two portable chargers in carry-on bags.

Airlines’ rules vary, leaving passengers to navigate different restrictions on their portable chargers from one airline to the next.

Delta matches the ICAO specifications, while United Airlines, which bans portable chargers and vapes from overhead bins, hasn’t prohibited power banks from being charged onboard. Meanwhile, Japan’s transport ministry and South Korea’s major airlines have banned passengers from using portable chargers in flight altogether.

Daniel Rodríguez, who commutes between Atlanta and Philadelphia, worries that a lack of compliance with portable-charger restrictions could lead to boarding-gate chaos. “If people don’t follow the rules, does it cause delays? Do we deplane?” he asked.

American and Southwest said they aren’t searching travelers to enforce their newest policies. Instead, the airlines are counting on passenger education, including cabin announcements and questions from gate staff.

Michael Massoni, safety chair for the Transport Workers Union Local 556 representing Southwest flight attendants, said passengers have reacted positively to the safety announcements he has delivered.

“The look that I’m seeing on their faces is not one of pushback or disgust,” Massoni said. “It’s more of, ‘wow, that makes sense.’”

Southwest plans to outfit its entire fleet with in-seat power by the middle of next year so that passengers won’t rely on portable chargers, said Dave Hunt, the airline’s vice president of safety and security.

Write to Amira McKee at amira.mckee@wsj.com