The medical device maker St. Jude Medical played down the failure of some batteries in its defibrillators, shipping them for years before recalling the devices last fall, according to a warning letter the Food and Drug Administration issued this week.

The company, acquired by Abbott Laboratories in January, also failed to tell its own management and a medical advisory board that the battery problems had led to the death of a patient, the agency found.

The F.D.A. said St. Jude Medical had not shown it was taking sufficient action to fix the problems that led to the slow recall and ordered the company to provide a new reporting plan within 15 days.

Faulty defibrillators and other implanted devices are particularly problematic because removing them requires surgery that can be more risky than keeping them in. When the company announced the recall in October, the F.D.A. recommended that doctors closely monitor their patients’ devices for problems. Saying the malfunction did not appear to be widespread, the agency warned that “patients could be at greater risk of complications from the surgical procedure required to replace the device.”

In October, the F.D.A. said that of the nearly 400,000 devices sold worldwide that were affected by the recall, 841 were returned to the company for analysis because the battery had died unexpectedly. As of January, two people had died because their defibrillators failed to work, the agency said, and dozens of others had suffered adverse effects. Defibrillators deliver an electric shock to return the heart to a normal pace when it is not beating properly.

An F.D.A. spokeswoman, Angela Stark, said Thursday that nearly 200,000 people in the United States have a defibrillator included in the recall. The recalled devices include models in the company’s Fortify, Unify and Assura defibrillator lines.

Physicians at Duke University reported two cases of battery problems with the devices in 2014, and another team at the University of Illinois did so in 2015, concluding that lithium in the battery was forming clusters and causing it to short-circuit. That same year, St. Jude fixed the problem in new defibrillators it manufactured, but it did not recall the older devices or alert doctors or patients about the potential problem until October. As a result, doctors continued implanting the old devices in patients.

“What bothers me most about this is that the doctors and the patients weren’t told about the potential” for failure, said Dr. Robert G. Hauser, a retired cardiologist who campaigns for improved safety of medical devices. “And clearly this is for St. Jude’s benefit. They can sell products rather than scrapping it.”

He also faulted the F.D.A. for not having investigated St. Jude earlier. “They should have been in there years ago, looking at all the raw data in order to determine if the incidence was low enough to allow these devices to be shipped and implanted,” he said.

Defibrillators accounted for nearly a third of St. Jude’s sales in 2015, or about $1.6 billion, according to The Minneapolis Star Tribune, which reported on the defibrillator issue last fall. In January, the company was acquired by Abbott for $25 billion.

Abbott said that it was reviewing the warning letter and that it was committed to addressing the issues raised by the agency. “We have a strong history and commitment to product safety and quality,” the company said.

Ms. Stark, the F.D.A. spokeswoman, said the agency did not insist on an earlier recall because it was relying on information the company had provided at the time. But while the agency now says the company misrepresented the risk, Ms. Stark said, “I don’t think we can speculate on how that might have changed the decision almost two years ago.”

According to the letter, St. Jude understated the problem by concluding that reports about failing batteries were “unconfirmed” even though the battery manufacturer, which the agency did not identify, concluded that the lithium clusters were the culprit. The company did not include these “unconfirmed” cases when it calculated the likelihood that the devices would malfunction, making it appear that the problem was less serious than it was, the agency said.

The agency also found that the company knew of a patient’s death in 2014 but did not disclose it to St. Jude Medical management or a medical advisory board. “Both presentations stated there were no serious injury or death directly related to lithium cluster formations,” the letter said.

In addition, the F.D.A. said that St. Jude still had not fully addressed concerns raised in January, when the agency warned that hackers could gain access to St. Jude’s defibrillators and remote monitoring system and could cause the devices to deliver unnecessary shocks.

This is not the first time a device maker has been accused of being slow to warn the public about a faulty defibrillator. In 2011, Guidant pleaded guilty to federal criminal charges and paid nearly $300 million in fines after it was revealed, in part because of Dr. Hauser’s efforts, that it had allowed some of its defibrillators to be implanted in patients even though the company knew the devices might short-circuit.

And that year, St. Jude came under scrutiny after it was accused of being too slow to recall faulty wires that connect the defibrillator to the heart.