Portable chargers have become the leading source of lithium-ion battery thermal runaway incidents on passenger aircraft, according to a new report from UL Standards & Engagement (ULSE).
The organisation's Lithium-ion Battery Incidents in Aviation: 2025 Data Review found that overall thermal runaway incidents increased 15% year-on-year, while incidents involving portable chargers rose 42%, surpassing e-cigarettes as the device most frequently linked to onboard events.
Drawing on incident data voluntarily shared by more than 40 airlines through ULSE's Thermal Runaway Incident Program, the report recorded an average of 2.36 passenger-related battery incidents per week in 2025, up from 2.05 a year earlier.
The findings come as airlines including United, Delta, American and Southwest continue to introduce or strengthen policies governing the carriage and use of portable chargers onboard aircraft.
ULSE estimates that lithium-ion battery incidents have cost commercial passenger airlines approximately $7.3 million between 2021 and 2024 through operational disruption, damage and associated losses.
"Every incident is a safety risk, and the trend line is moving in the wrong direction," said Jeff Marootian, president and CEO of UL Standards & Engagement.
According to the report, passenger awareness remains a key challenge, with the organisation calling for greater industry efforts to educate travellers on the safe handling and storage of rechargeable devices during flight.
