KUALA LUMPUR - An 'alien' substance was mixed into the production process of the battery that caused a Dell customer's notebook to burst into flames and prompted a recall last week.

"As a result of analysis, we defined the cause of the short circuit that occurred in one cell was due to mixing of an alien substance at one production process," said Yoshiyuki Arikawa, a spokesperson of battery-supplier Soft Energy Company, a unit of Japanese consumer giant Sanyo Electric Co Ltd.

In the e-mail response to ZDNet Asia, Arikawa did not define what the 'alien' substance could be or how it entered the production process. Bloomberg, quoting another Sanyo spokesperson, reported Tuesday that "a piece of metal found its way into the battery."

Arikawa added, "The defect rate should be very small since it’s a specific occasion and (went through) normal inspection process after. The defect is limited only to the 27,000-set lot to Dell."

Dell Computer recalled the 27,000 batteries with a promise to replace them free of charge. The batteries were shipped in several models of Inspiron and Latitude notebooks to customers in North, Central and South America from June 22 through September 15, 2000, and in Europe, the Middle East and Africa from June 22 through October 4, 2000.

Arikawa said no other notebook manufacturers supplied by Sanyo were affected.

Sanyo is the world's largest manufacturer of rechargeable batteries, used in a variety of applications including cellular phones, PDAs and video cameras.

The incident that triggered the recall happened to a US corporate customer at the end of August. The battery overheated and the notebook started smoking. When office staff took it outside it apparently burst into flames. No one was injured in the incident.

Arikawa confirmed that the battery was a cylindrical-model Lithium-Ion. "Lithium-ion cells have two or three protection systems in the cell and normally this would not happen. In this case, it is very rare. We already have put countermeasures in place to prevent a recurrence."

Sanyo and Dell have not indicated why it took more than a month to recall the faulty units.

A Lithium-ion battery of unknown make was pinpointed for causing an Apple Powerbook 5300 to burst into flames at a Singapore plant in 1995.