The National Institute of Technology and Product Evaluation (NITE) said Wednesday that leaving mobile batteries on car dashboards during summer can cause fires.

This alert comes as rising summer temperatures turn vehicle interiors into hazard zones for lithium-ion batteries. Because these devices are common for commuters and travelers, a single forgotten battery can lead to a total vehicle loss or wider parking lot fires.

NITE said that dashboard surface temperatures can exceed 70°C [2] during the summer months. When mobile batteries are exposed to this extreme heat, they can overheat and expand, leading to internal short circuits and subsequent ignition.

The agency cited a specific fire incident in a parking lot in Sendai, Miyagi Prefecture. In that case, the fire occurred even though the maximum outside temperature was only 28°C [3], demonstrating that internal car temperatures can be dangerously higher than the ambient air.

Statistical data underscores the scale of the risk. Between 2020 and 2026, there were 2,140 reported accidents [1] involving products equipped with lithium-ion batteries. The data indicates that August is the month when these accidents occur most frequently [4].

To highlight public behavior, a survey of 1,406 people [5] was conducted regarding the handling of mobile batteries during the summer. The findings emphasize the need for users to store electronics in cooler areas of the vehicle, or remove them entirely when parked in the sun.

NITE said the risk is not limited to low-quality products, as the physics of heat-induced battery failure affects the chemistry of lithium-ion cells generally.

“Dashboard surface temperatures can exceed 70°C during the summer months.”

The warning highlights a critical gap between ambient weather reports and actual vehicle conditions. While an outside temperature of 28°C may seem mild, the greenhouse effect within a parked car creates a microclimate capable of triggering thermal runaway in batteries. As the adoption of high-capacity portable power increases, these incidents are likely to persist unless consumers change storage habits.