Just a point on this, in the two UK apple stores I went into recently, they were literally crammed with people getting replacement batteries. At least three people’s battery change didn’t work (including the screen repair I was getting done due to a white spot on the display) and they handed over brand new iPhones to those people. This has a significant cost to it which multiplies the original problem somewhat!

It’s extremely obvious they weren’t ready for this quantity of repairs.