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NTT DoCoMo and Mitsubishi Electric are planning to replace around 1.3 million batteries manufactured by Sanyo Electric because they may overheat and catch fire, the companies said today.

The batteries were manufactured before June 2006 and are used in NTT DoCoMo's D902i handset. Some may have also been used in two other Mitsubishi Electric models, the D902iS and D903iS, the companies said. The batteries carry the model number D06.

"In rare cases there is a slight deformation of the electrode plate which causes it to come into contact with the insulation sheet and hence the insulation sheet can become damaged," said Richard Sedgwick, a spokesman for Sanyo in Tokyo. "If the battery was also damaged through an outside side, for example if the user dropped the battery, then the problem could occur."

Possible Issue Recognized in April

NTT DoCoMo said it has confirmed one case of the battery rupturing because of the problem and knows of 17 other cases where the D06 battery has ruptured or overheated. The carrier said the battery had been subject to an "extremely strong impact" in a number of the cases.

Sanyo said it began examining ways of strengthening the electrode in April this year as a precautionary measure against possible problems, but at the time had not heard any reports about actual problems. Batteries with stronger plating on the electrode began rolling off the company's production line in June, hence today's advisory only concerns batteries manufactured until May.

Similar to Sony Problem

The problem brings back memories of Sony's battery problems of earlier this year. Around 9.6 million Sony-manufactured laptop computer batteries were recalled or voluntarily replaced by many laptop PC vendors after batteries in several PCs overheated and caught fire. The problem was traced back to metal particles that had gotten into the battery during manufacturing.

Sony estimated the problems will cost it around $444 million this financial year.

Sanyo said that it has yet to work out with NTT DoCoMo and Mitsubishi Electric the part it will play in the replacement.

Sanyo and Sony are two of the world's largest manufacturers of lithium ion batteries.

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