Japan’s trade ministry has in investigating a possible battery defect in the first-generation Apple iPod nano digital media player in the wake of fires that have caused minor property damage and injury. According to the trade ministry, it is aware of three fires caused by overheating iPod nanos which caused no injuries but burned paper and a tatami mat. However, the ministry also says Apple has reported additional incidents, including two cases where users had suffered minor burns. In all cases, the iPod nanos apparently overheated while being recharged, and officials are apparently looking into the possibility of a defect in the lithium-ion batteries used in the units.

The trade ministry has issued a warning to iPod nano owners warning about overheating, particularly when recharging the units.

The iPod nanos in question are no longer sold, having long-since been replaced by the video-capable second-generation iPod nanos. (Which are, themselves, about due to be refreshed.) According to the Japanese trade ministry, the first-generation nanos in the overheating incidents were sold in Japan between September 2005 and September 2006, and carry the model numbers MA004J/A, MA005J/A, MA099J/A and MA107J/A. The trade ministry did not identify the manufacturer of the batteries in the affected nanos, nor offer any indication if the same manufacturer also made batteries used in iPod nanos in the rest of the world.

The ministry has ordered Apple to investigate the cause of the problems, but there are no indications Apple is currently considering a recall.