It's a new scare for millions of computer users.
Photos of a Dell laptop computer on fire at a conference in Japan have caught many people's attention.
Now, no one is certain how big a threat this really is.
"This is a very serious concern -- potential for a laptop computer overheating," said Nancy Nord of the Consumer Product Safety Commission.
Dell's record recall of 4.1 million laptop PC batteries was prompted by six incidents of the Sony-made batteries overheating.
No injuries have been reported, but Dell is apparently not yet counting a case in July, in which a man who says his Dell laptop set his vintage pickup truck on fire.
Consumeraffairs.com has reported on that case and others.
"Put that same laptop on an airplane, 30,000 feet up in the air and who knows what's going to happen," said Joe Enoch of Consumeraffairs.com.
The Wall Street Journal reports that Transportation and Safety Administration officials are so concerned about the risk of fire that they have said, "Batteries in laptops … pose a serious risk to airplanes."
It's not just Dell batteries.
In a frightening incident in February, a UPS cargo plane at 31,000 feet caught fire.
Miraculously, the plane landed safely with no one hurt.
The suspected cause of the fire: lithium-ion computer batteries.
Lithium-ion batteries pack power in a small package, but if defective, can short-circuit and catch fire.
An Iowa family says in April its son's Apple iBook laptop made a popping noise, filled the room with smoke, and then burst into flames.
A former Dell employee, Robert Day, who quit after an unrelated dispute with the company, says he saw many more melted laptops at company headquarters than Dell has acknowledged.
He doesn't know whether they were caused by battery problems.
"Basically I saw an increase of product coming from the field for safety issues," Day said. "But some of the laptops I saw did have some battery damage, did have some thermal damage as far as melting."
Dell says that the reported incidents are very rare and that the safety of its customers is its top priority.
The Consumer Product Safety Commission says consumers should not use the recalled batteries for now.
"Our concern is that consumers not use these batteries, that they take them out of their computer," Nord said.