The Asahi Shimbun reports that according to its sources, Matsushita Battery Industrial Co. knew from as far back as May that a defect could cause its cellphone batteries to overheat.

Defective Matsushita batteries used in Nokia phones have already overheated and caused two accidents in Japan alone. On Tuesday, Nokia announced a worldwide recall of around 46 million defective batteries.

According to the Asahi Shimbun's sources, Nokia informed Matsushita Battery back in December 2006 of a possibility that its BL-5C lithium-ion battery could overheat. In May, Matsushita discovered that a glitch during the manufacturing process led to a short circuit in the battery which could then cause overheating.

Matsushita did not reveal the problem publicly but did inform Nokia. The latter was, according to the report, "apparently reluctant to disclose the fact".