As many as 11 million people reportedly swapped out their batteries last year, when replacement prices were cut to $29. Normally, the annual number is between 1 and 2 million.

The news follows Apple’s surprise note to shareholders on Jan. 2, in which Cook revised the company’s revenue guidance for its first fiscal quarter from an expected range of $89 billion to $93 billion to $84 billion.

In that note, Cook pointed to slower sales in China, but also hinted at some domestic issues, writing ” While macroeconomic challenges in some markets were a key contributor to this trend, we believe there are other factors broadly impacting our iPhone performance, including consumers adapting to a world with fewer carrier subsidies, US dollar strength-related price increases, and some customers taking advantage of significantly reduced pricing for iPhone battery replacements.”

Apple did not immediately reply to Fortune‘s inquiry seeking to verify the number of replaced batteries.

If the 11 million figure is correct, though, that’s still a bit better than some early estimates feared. Last January, analysts warned that the vast number of people eligible for the battery offer could result in as many as 16 million missed iPhone upgrades in 2018.