Here we go again. Toshiba is urging its customers to trade in potentially flammable laptop batteries, after a Toshiba notebook caught fire on 24 May this year. The battery that burst into flames was a Sony battery cell that should have been returned last year.

Toshiba was one of the laptop vendorsthat, last year, recalled more than 8 million rechargeable lithium-ion batteries made by Sony. A manufacturing defect left those laptop batteries vulnerable to short-circuiting and catching fire if they were jostled.

Dell was the first to recall those batteries in August 2006, quickly followed by Apple, Lenovo, Fujitsu, Gateway and Sony. By October 2006, that defect had led to 16 reports of notebook computer batteries overheating, causing minor property damage and two minor burns.

On Tuesday, Toshiba said the latest fire was sparked by a battery that was never returned. Later in the day, Gateway recalled laptop batteries made by Samsung.

In the original recall, laptop users were warned to remove the batteries immediately and to power their PCs only by plugging them into a wall outlet until receiving a free replacement battery from the PC manufacturer. Laptop users were responsible for taking the initiative to return their own batteries, leading some analysts to predict that only a small percentage would do so.

"Recently, certain instances occurred where Sony battery packs installed in Toshiba portable computers caught fire," Toshiba said on its website. After an investigation with Sony, Toshiba found that the battery caused the situation, the statement said.

"The original Sony Battery Pack had not been replaced as recommended by Sony and Toshiba.

"We put importance on the fact that the incidents that occurred involved unreplaced Sony Battery Packs, despite our ongoing replacement program."

Other PC vendors may face the same challenge. Dell is continuing to replace the faulty batteries, but a spokesman said he could not produce figures for the number of batteries replaced or whether the company had noted any overheating incidents since the recall began.

"The recall's going well. Customers are taking heed to send back the affected batteries and have replacements sent to them," said Dell spokesman Bob Kaufman.

In response to the latest fire, Toshiba warned customers to stop using the affected batteries immediately. Users who continue running their laptops on battery power should not leave their PCs unattended while they charge and should not place PCs on a sofa, bed or other surface that could obstruct its ventilation, Toshiba said.

Toshiba has not changed the list of laptops that use the affected batteries. They include various models of the company's Portege, Qosmio, Satellite and Tecra brand PCs. As with the original recall, Toshiba will replace all affected batteries for free.