A Japanese independent administrative agency has warned consumers that products powered by lithium-ion batteries, such as portable chargers and handheld fans, are more liable to catch fire during summer.

A survey by the National Institute of Technology and Evaluation, or NITE, showed that the number of accidents involving such devices has been increasing in recent years, to 1,860 between 2020 and 2024. Fire accounted for 85% of them.

Lithium-ion batteries are vulnerable to heat and impact, making them prone to accidents when temperatures rise.

August marked the highest number of accidents, at 228 cases in the five-year period, followed by July, at 212, and June, at 201.

By product, portable chargers logged the highest number, at 361 cases. There were 202 accidents involving power-assisted bicycles and 171 for rechargeable power tools.

In July 2020, a man in his 50s in Hyogo Prefecture suffered minor burns when a handheld fan made a strange sound and caught fire while it was being charged.

In August 2023, a man in his 40s in Kumamoto Prefecture saw his portable charger overheat and ignite after it was left in the driver's seat of his car for hours.

If a battery expands or becomes unusually hot, users should immediately stop charging it or using the device powered by it, NITE said.

It said that if a battery ignites, users should extinguish the fire with a large amount of water and notify fire authorities after submerging the device if possible.

NITE said that the spread of cheap, copycat batteries with insufficient safeguards may be behind the increase in cases of spontaneous ignition. People should check sellers' contact information and any recall notices before buying devices, it said.