But in June the battery in a Dell laptop computer caught fire during a conference at a hotel in Osaka, Japan. Pictures of the burning computer spread on the Internet.

In the last few weeks, other laptop owners learned that they had good reason to be concerned. Dell and later Apple Computer recalled millions of lithium-ion batteries that could overheat and create a risk of fire. 

Dell asked the owners of more than four million notebook computer batteries to return them for replacement. More than one million of these batteries were sold outside of the United States.

Apple recalled almost two million batteries used with some of its notebook computers. Seven hundred thousand of them were sold in other countries.

The United States Consumer Product Safety Commission announced the recalls. It described them as the two largest recalls in its history involving the consumer electronics industry.

Agency officials said Dell had received six reports of batteries overheating. These resulted in property damage but no reports of injuries. The agency said Apple had received nine reports of overheated batteries. These included two reports of minor burns and reports of minor property damage.

In Japan, officials have ordered the two companies to investigate reports of fires in at least two Dell laptops and one Apple laptop.

Sony of Japan made the millions of recalled batteries. Sony officials say a production problem left very small pieces of metal that could cause a short-circuit and make a battery overheat.

Experts from different companies plan to meet in California this month to discuss the manufacture of lithium-ion batteries.

As laptop computers have gotten more powerful, they require more powerful batteries. Yet batteries are still not powerful enough to satisfy many users.

Some people see microcell technology as a solution. Microcells use energy sources like hydrogen and methanol. Many companies are working to find ways to make them safe and useful for computers. Experts say it could be ten years before computers with microcells are widely available.