Sony has provided greater detail about a battery-manufacturing problem that is expected to see the replacement of up to 9.6 million laptop computer battery packs.The problem was first acknowledged in August when Dell issued a recall for 4.1 million batteries and until now had been explained as metallic particles that got into the battery during the manufacturing progress. On Tuesday, Sony expanded on this and said the particles, believed to be nickel, likely got into the battery during two stages in production: when a groove was created in the battery case and when the electrolyte was poured into the cell.But that alone wouldn\u2019t be enough to cause the fires that have been reported by laptop owners. For that to happen, Sony believes the particles would have to fall into a small triangular gap in the cell body right at the point where the cathode ends between two layers of spacer material. Then, depending on system configuration, the conditions could be right for a fire to start in the battery."The probability of this occurrence very much depends on system configuration," said Takashi Enami, senior general manager of the energy business group at Sony. He said size and shape of the battery pack and the charging configuration could all increase the risk, but he wouldn\u2019t offer any specific information, citing confidentiality agreements between Sony and its customers.As a result of the problems, 6.1 million batteries have been recalled by Dell and Apple Computer. An additional 3.5 million batteries are covered by a Sony-led replacement program that offers new batteries to laptop users who are worried about the safety of their system. Last week, Sony said it anticipates costs of 51 billion yen (US$427 million) as a result of the battery problems.The replacement program covers two types of cells used in battery packs\u2014a 2.4Ah (ampere hour) and 2.6Ah model\u2014and information on the affected battery packs and laptop PC models sold in the United States can be found at the U.S. Consumer Product Safety Commission (CPSC) homepage.Sony considered the battery replacement after a Lenovo-made laptop caught fire at Los Angeles International Airport, said Yutaka Nakagawa, executive deputy president of Sony and head of its semiconductor and component group. That incident is still under investigation, and as only two of the six cells inside the battery pack remain, it\u2019s difficult to pinpoint the exact cause, he said."In preparing for the program, we have been in discussion with the CPSC and the PC manufacturers, which required time, and that is why the announcement is being made today," said Nakagawa.The replacement batteries won\u2019t all come from Sony because it doesn\u2019t have the manufacturing capacity to produce them all in the time required, said Nakagawa. As a result, Sony will source some cells from rival companies. Nakagawa said as a result there is a general possibility that Sony might not win back all the business it had before the battery problems occurred. Its success or failure in keeping business very much depends on how well Sony does to persuade customers that the problems are behind it, he said.Sony also increased the number of its own battery packs eligible for the replacement program. Last week it said 60,000 batteries used in PCs in Japan and China would be replaced, and on Tuesday increased this to 250,000 batteries worldwide.By Martyn Williams, IDG News Service (Tokyo Bureau)Follow CIO.com\u2019s ongoing coverage of the battery recall story.Check out our CIO News Alerts and Tech Informer pages for more updated news coverage.