Based on its conversations with Dell, Sony strengthened and reinforced the protective barriers and lining of their battery cells to address the danger of metal particles piercing the lining of the cell, Clancy said.

Dell is reported to have known about incidents of laptops overheating, albeit in small numbers, for years. It and CPSC recalled 22,000 laptop batteries in December, 2005, because of overheating problems. Metal particle contamination was the cause behind that recall, as well, said Scott Wolfson, a CPSC spokesman.

Those units were sold between October 2004 and October 2005. Sony declined to characterize the discussions between the companies that took place in October, 2005, and then again in February, except to say that they were "specific to particular cells of batteries in battery packs used in Dell notebooks," Clancy said.

Doughty said Li-ion batteries usually fail "benignly," in what researchers call a "soft short," in which a low current path is created within the battery that causes it to discharge its energy into the cell. However, if a large particle of conductive material penetrates the separator, connecting the anode and cathode, or a small particle of conductive material manages to find just the right position between the anode and cathode, a "hard short" can result in which the battery cell releases all its energy at once, in what's called "thermal runaway."

The key in situations like that is to prevent the reaction from spreading to other cells in the battery pack, which appears to have happened in the now-famous incident in June in Osaka Japan, he said.