We all remember the throttling scandal Apple went through last year, when the company decided to slow down some models to compensate for battery performance degradation. As an apology, Apple decided to lower the price of iPhone battery replacements from $79 to $29. What the iPhone-maker didn’t predict was the huge number of batteries it would have to replace.

There was an all-hands meeting discussing results with Apple employees, the contents of which have still not leaked. Except for this bit: Apple replaced 11 million iPhone batteries during the duration of the $29 replacement program. Normally, Apple would replace 1 to 2 million batteries during the same period of time, meaning almost ten times as many users decided to just replace batteries opposed to upgrading.

My guess: the effect of the battery replacement program on new iPhone sales wasn’t apparent until after the iPhone XR and XS models were available. A few million extra iPhone users happy with the performance of their old iPhones with new batteries — who would have otherwise upgraded to a new iPhone this year — put a ding in the bottom line.

Apple only saw the effects of this once the 2018 iPhones were out. iPhone Xs, Xs Max and Xr models experienced weaker sales because customers were still happy with the performance of their older models, now rocking brand new batteries.