NTT DoCoMo and Mitsubishi will replace 1.3 million Sanyo phone batteries due to overheating and fire concerns.

The batteries were manufactured before June of this year and are used in DoCoMo's D902i handset and possibly Mitsubishi's D902iS and D903iS. 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 a Sanyo spokesman. "If the battery was also damaged through an outside side, for example if the user dropped the battery, then the problem could occur."

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 that the problem only concerns batteries manufactured until May.

The problem is reminscent 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 got into the battery during manufacturing.

Sanyo and Sony are two of the world's largest manufacturers of Lithium Ion batteries.