Defective batteries and a software glitch in one of Zoll Medical Corp.‘s defibrillators may have killed two people, the Chelmsford device maker warned.

Zoll issued a “voluntary worldwide field corrective action” on its AED Plus automated external defibrillator after discovering the problem.

Batteries in some of the devices made before Feb. 12 are defective and the software in the debrillators that’s supposed to detect such problems doesn’t work properly. The roughly 180,000 affected devices carry serial numbers below “X_ _ _200000,” the company said, adding that defibrillators older than three years — about 80,000 of them — are the most likely to fail.

The problem came to light from customer reports, according to a press release, and “there has been one clinical event reported in which a defibrillation shock was not delivered [and] the patient subsequently died.”

A subsequent review found that three other devices failed and, in one of those instances, a second patient later died.

The software defect can be fixed with a patch, availabe for download from the company’s website, that can detect defective batteries and alert users.

Zoll said the federal Food & Drug Administration is expected to issue a formal recall.