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.