https://www.cnbc.com/2019/01/15/apple-upgraded-10-to-11-million-batteries-according-to-report.html

Apple replaced 11 million iPhone batteries during the length of its battery replacement program, even though it only expected to replace about 1-2 million of them, according to well-connected Apple insider John Gruber.

Apple CEO Tim Cook revealed the figure during an all-hands meeting that was first reported by Bloomberg.