TORONTO - A defibrillator company is reporting problems with a warning light that indicates when the battery in the product is low, Health Canada said Thursday.

Defibtech has sent notices to customers to warn that version 2.002 and earlier versions of the software in the DDU-100 series Automatic External Defibrillators require an upgrade.

Ray Valek, a lawyer for the company, said a worldwide recall affects 42,000 units, including an estimate of fewer than 1,000 in Canada.

The defibrillators are most often found in public areas, schools, health clubs, manufacturing plants and stadiums, as well as in police and fire vehicles, he said.

They're seldom purchased by homeowners, he noted.

Valek said that in some situations, self-test software on the devices might "clear" or fail to warn of a previously detected low-battery condition.

"For example ... an operator will do a self-test for a low battery and it basically will say there is a low battery - but then for some reason that individual might not change the battery because he maybe forgets about it or puts it off, or whatever," Valek said in an interview from La Grange, Ill.

"And then a month later, he runs another test and the device won't identify the low-battery condition a second time."

If this occurs, the operator may be unaware of the low battery, and the device might not deliver a shock to restart someone's heart in an emergency.

Valek said that until the software problem can be fixed, those who have the defibrillators are encouraged to run low-battery tests on a more frequent basis to make sure the battery is delivering enough power. Instructions are contained in the letters that have been sent to customers.

The company voluntarily determined the need for corrective action after three reports of malfunctions, he said.

The units don't need to be returned or replaced. Rather, new software, when it's ready, will either be delivered to the end user, or it will be something that can be downloaded, Valek said.

Distribution of the new software may take 12 to 16 weeks, the company said in letters to customers.

The batteries normally last more than three years, the company said, and problems are more likely when a battery is near the end of its life.