Toshiba, Fujitsu and Dell recalled more Sony-made laptop batteries Friday, swelling the number of units involved in the massive global recall to more than seven million.

Early Friday, Sony Corp. formally asked manufacturers using its problem batteries to carry out a recall.

Sony has said the batteries could pose a risk of fire in rare cases when microscopic metal particles generated during manufacturing come into contact with other parts of the battery cell, leading to a short circuit.

Typically a battery pack will power off when there is a short circuit, but on occasion the battery can catch fire.

As a result of the request, Toshiba Corp. is recalling 830,000 Sony-manufactured batteries for its notebook computers. Dell Inc. boosted its own recall by 100,000 for a total of 4.2 million.

Fujitsu Ltd. is recalling an undisclosed number of Sony batteries that are used in 19 of its laptop models, according to Fujitsu spokesman Masao Sakamoto.

Toshiba spokesman Keisuke Omori said Toshiba had not found any cases in which its laptops were at risk of catching fire.

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