Firefighting authorities in Tokyo say a record-high number of fires caused by lithium-ion batteries were reported in the Japanese capital last year.

The Tokyo Fire Department says a preliminary report shows there were 382 cases of fires involving products using the batteries in 2025. That's up 139 from the previous high recorded a year earlier.

Lithium-ion batteries are used in portable chargers, smartphones, personal computers and other rechargeable products. The batteries contain a flammable organic solvent. They can generate heat, explode or catch fire at high temperatures or if subjected to strong impact.

By product, 130 of the reported cases involved portable chargers, 43 cases smartphones, 25 cases power-assisted bicycles and seven cases portable electric fans.

Similar fires have been occurring this year. On Monday, a portable charger in a train passenger's backpack caught fire on a private railway, slightly injuring a woman nearby.

Officials say such fires often occur during summer, with about 40 percent reported from June to September.

Officials also analyzed the causes of fires using data from 2022 to 2024. The data show about 22 percent of the cases occurred during normal use and about 11 percent during dismantling or disposal. Roughly 10 percent were attributed to external shock.

The department says as temperatures are rising, people should avoid applying shock to portable electric fans and other items that use lithium-ion batteries. It is also calling on people not to leave such products in hot places, such as on car dashboards.