SEOUL- Replacement batteries for Samsung's troubled Galaxy Note7 smartphone have been overheating and quickly losing battery power, some consumers have complained, as the South Korean technology giant struggled with the unprecedented recall of its premium smartphone.

The company acknowledged Friday (Sept 23) that some customers had been complaining about the replacement smartphones, which contain non-removable replacement batteries, reported the Wall Street Journal.

Samsung began handing out replacement smartphones to consumers only on Monday.

On Thursday, South Korean television news network YTN began reporting incidents of newly exchanged smartphones overheating or losing battery power even as they are being charged, WSJ said.

It added that the complaints have been registered only in South Korea. The company declined to confirm if similar cases were found in other countries.

According to the WSJ, a Samsung spokesman said Friday that the issue is "completely unrelated to batteries", calling the incidents "isolated cases" related to mass production issues.

He added that the company was conducting "close examinations" of the issue.

The world's top smartphone maker announced earlier this month a recall of at least 2.5 million Note7s across the globe due to faulty batteries causing some of the phones to catch fire.

Samsung declined to comment on how many phones are being recalled in South Korea, but the firm's report to the Korean Agency for Technology and Standards dated Sept 2 seen by Reuters showed that 429,000 Note7 phones had been sold prior to the recall.

Shares in Samsung, which plans to resume new sales of the Note7 in South Korea on Sept 28, closed 2.9 per cent lower Friday following YTN's report after five straight days of gains, WSJ said.