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."