Apple has confirmed to The New York Times that a “very limited” number of iPhone 5s units could experience shortened battery life as the result of a manufacturing problem.

The exact number of affected units is not clear, but the statement is said to imply that the number is in the few thousands range. Apple sold 9 million iPhones total over its opening weekend. The NYT notes that a manufacturing problem does not equal a defective battery, so it is unclear what the actual source of the issue is.

Affected users can expect to be contacted by Apple soon and will be issued a replacement phone.