I have my appointment set for 1/4 as I thought many will be taking advantage of this. I called, and you would not believe the hassle I got. I was told by an Apple employee, they would not replace the battery if it's not needed!! What? I'm paying for the replacement, it's not up to you to tell me if I need the replacement or not, I want to pay for the replacement. We went round and round. Finally, after talking to 3 higher level people each time, they agreed to set up the appointment. They will check your battery and may push back if it does not need replacement (the battery shows it's OK) - but you don't know what will happen in a year from now (replacement for $30 ends Dec 2018), so if you think you need replacement, do it sooner than later.