The world's largest manufacturer of personal computers, Dell, is to recall 4.1 million of its notebook computer batteries because of a fire risk.
Nobody is thought to have been injured by one of the batteries
Most batteries are in computers sold in the US but more than 1 million are thought to be elsewhere.
Dell says it knows of six instances since December when the batteries, made by Sony, overheated or caught fire.
The US body responsible for consumer safety says it is the biggest recall of electrical products in its history.
Alex Gurzen, the vice-president of Dell's product group, told the BBC the firm wanted to "put customer safety first despite this being a small handful of incidents".
He said the 4.1m battery packs being recalled represented "about 15% of the batteries that we sold" over the affected period between mid-2004 and this year.
He denied that the move would affect Dell's earnings.
Dell is offering affected customers free replacements.
A spokesman for the Consumer Product Safety Commission (CPSC), Scott Wolfson, said users of affected laptops should only run the machines on a power cord.
The Sony lithium-ion batteries were placed in laptops shipped between April 2004 and July 2006.
They were included in some models of Dell's Latitude, Inspiron, XPS and Precision mobile workstation notebooks.
"In rare cases, a short-circuit could cause the battery to overheat, causing a risk of smoke and or fire," said Dell spokesman Ira Williams.
"It happens in rare cases but we opted to take this broad action immediately."
Dell has already launched a website - http://www.dellbatteryprogram.com - telling customers how to get a free replacement battery.
No injuries had been linked to Dell laptops with defective batteries, the company told Reuters news agency.
The CPSC has identified 339 incidents in which lithium batteries used in laptops and cell phones - not just Dell products - overheated between 2003 and 2005.
Some incidents involved minor skin burns or actual injuries as well as property damage, Mr Wolfson said.