Apple says that it replaced around 11 million iPhone batteries last year, according to information leaked from in a recent meeting headed by CEO Tim Cook.
Apple was only expecting to replace 1 to 2 million batteries last year, according to the post by the leak's publisher, Daring Fireball’s John Gruber. This context makes this already large number appear even larger. Considering that Apple was offering $50 off replacements for the entire year, it’s perhaps not that surprising in retrospect.
Apple dropped the price of its battery replacement service from $79 to $29 in 2018, by way of apology for its decision to throttle the performance of aging iPhone batteries without informing users. Its reasoning for this was to prevent inconsistent performance or damage to the phone, but many outside the company were unconvinced, believing it instead to be a form of planned obsolescence.
The company recently warned that earnings are not at expected levels, revising its estimates downwards by $5-$9 million in a letter to shareholders. It blamed a lack of demand in China and fewer upgrades due to users making use of the discounted battery replacement as some of the causes.
Gruber himself suggests that this drop might have surprised Apple itself, since its November earnings report had a more positive outlook. He posits that Apple didn’t really notice the drop in sales until its most recent models, the iPhone XR and iPhone XS, went on sale, rather than the company trying to hide its poor figures. It's possible that the new, lower-cost battery replacement program encouraged users to stick with their older phones, rather than spring for the new 2018 models.