The largest computer-product recall in U.S. history has sent scores of consumers scrambling to pry open their laptops and check if they have batteries that might overheat.

Acting on a potential fire hazard discovered in lithium-ion battery cells that power several of its notebook computer models, Dell Inc. began exchanging 4.1 million of the batteries sold world-wide, including 2.7 million batteries in the U.S.

The announcement, in conjunction with the Consumer Product Safety Commission, came amid increasing concern about the dangers of lithium-ion batteries for portable electronics carried aboard aircraft.

The Consumer Product Safety Commission has recorded 339 cases of lithium and lithium-ion batteries made for laptops and cell phones overheating, smoking or catching fire since 2003. Laptop batteries have accounted for 176 of them.

As word of the Dell recall spread, some owners who already have experienced trouble with their laptops acted fast. "I had been having problems with it getting really hot," says Evan Spiegel, a Ph.D. student at Cornell University in Ithaca, N.Y. Mr. Spiegel, 23 years old, ordered a replacement battery for his Dell Inspiron 9300 online early Tuesday morning on Dell.com.

Here are answers to some common questions about battery safety being raised by the recall:

Q: I don't have a Dell laptop. Should I worry?

A: Since laptop batteries are tailored to individual machines, the recalled Dell batteries won't surface in other devices. But the faulty batteries were made for Dell machines by a unit of Sony Corp., which also supplies batteries to other PC makers - raising the possibility of more recalls.

Numerous other computer makers, including Apple Computer Inc. and Hewlett-Packard Co., already have recalled batteries in recent years. To see if your battery needs replacing, visit the Consumer Product Safety Commission home page at cpsc.gov and search for recall notices by company.

Q: Are there any precautions I can take in transporting or storing my laptop?

A: Computer bags or cases with ample padding should do. Many computer makers sell bags tailored to the size of their laptops and thus offer the best cushion. As for spare batteries, cover or wrap them in a nonmetallic substance such as a cloth or blanket or other fabric. Take care with battery contacts - the external points containing the positive and negative terminals that connect to the laptop itself. Cover them with tape.

Q: Is recharging a potential hazard?

A: Yes, primarily in older batteries, counterfeits or replacement batteries purchased separately from the laptop and often from sellers (Internet, small storefronts and kiosks) that offer no supporting information about the product or its maker. These batteries can lack circuitry that vents excess heat or shuts off the battery before overheating.

Problems arise when the battery doesn't power down once it regains its full charge. Electricity continues to generate heat and causes what experts call "thermal runaway," when a build-up of heat explodes out of control.

Q: I have a Dell laptop. How do I tell if I have a recalled battery?

A: Dell has set up a Web site, www.dellbatteryprogram.com, that provides details. The recall only affects some batteries used with some models of its Latitude, Inspiron, Precision and XPS laptop computers. They may have come with the computers, been purchased as secondary batteries or installed in connection with service calls.

Consumers should first check to see if they own one of the computer models listed on the Web site. If they do, they need to check to see if they have one of 36 battery models listed on the site, which describes where to find the model number on the battery and asks users to enter their specific battery identification number into a form. If the battery is subject to this recall, users are directed to a replacement order form.

Q: How do I remove and dispose of a recalled battery?

A: The recalled batteries come in all shapes and sizes. If your battery is attached to the back of your device, unclip it, or take it out if it's inside. Dell is requesting that the customer return all recalled batteries to the company so that they can be disposed of properly and will provide prepaid return packaging with the replacement battery. Consumers can also find battery recycling drop-off locations through Earth911.org and through Rechargeable Battery Recycling Corp. (RBRC.org). The company advises owners of affected batteries not to use them while awaiting a replacement. Users may continue to use the notebook computer, however, by ejecting the battery and using the AC adaptor power cord.

Q: How can I get a new one?

A: With Dell's battery-replacement hotline currently swamped (866-342-0011), the easiest way is online. Once you have determined that your specific battery is affected by checking your model and piece identification number at Dellbatteryprogram.com, you can order a replacement battery at no charge through a link on the bottom of the same verification page. Consumers are prompted to provide their name, shipping address and email addresses, where they receive a notification once the order has shipped. The company says most batteries should arrive with 20 business days or sooner although times may vary.

Q: Should I worry about the lithium-ion batteries in my cellphone, camera and other gadgets?

A: Overheating incidents have occurred in all portable electronics powered by lithium-ion sources. Before Dell's current recall, Dell and dozens of other makers had recalled a total of 1.46 million such batteries since 2003. In that span, more than 339 overheating incidents were reported involving batteries for everything from laptops and cell phones to MP3 players, cameras, flashlights and more.

Product owners should periodically visit the recall data base at the Consumer Product Safety Commission's Web site, where they can search by brand name or product description. If the battery came with the device at purchase, the relevant recall would be logged under the company that made the device. If the battery was bought separately, a recall would be found under the name of the specific battery maker.

Q: How can I stay abreast of future recalls?

A: Regularly check your computer manufacturer's homepage for recall notices, keeping an eye out for new and updated links tucked to the side and bottom of the page. Visit the Consumer Product Safety Commission homepage at cpsc.gov. The agency - which works with manufacturers to issue safety recalls on thousands of consumer products - posts releases that can be sorted by month as well as product type and company. Registering your device will also increase the likelihood that the manufacturer will contact you directly in the event of a recall. Dell is preparing to contact consumers whose email and addresses it has on record once call volumes start to subside.

Q: Other than battery defects, what other conditions can trigger overheating, smoking, fires?

A: Regulators are most concerned about the compatibility between batteries and devices. Many replacement batteries marketed as compatible with a range of products aren't, perhaps causing a short-circuit or fire hazard. The agency recommends buying batteries and other accessories of the same brand as the company that made the device.

Perhaps the greatest safeguards are proper use and handling. A fall or jostling may violently disrupt circuits.

Charged Issue

Precautions that consumers can take with laptop batteries:

- Keep the laptop and spare battery from coming in contact with metal, which conducts electricity and can cause the positive and negative terminals to cross, short-circuit and then spark.

- Don't expose either the laptop or the spare battery to extremely high temperatures.

- Don't pack the item in tight quarters that may apply pressure. Enough impact can burst the battery cell and ignite it.