I paid for battery replacement on my 2012 MBPr (the first generation) and got the top case replaced free because "they changed the design of the battery and it wouldn't fit in the old top case"
edit: mandatory bitching about people who put Apple on a pedestal - AppleCare only covers the battery up to 1000 cycles. Mine was at 1080 cycles. Time to open the wallet.
Ehh, that's still better than what used to happen when they had removable batteries. Back then it was 300 charge cycles and I constantly had batteries that would give service errors well below that, but because they were over a year old they were out of warranty. I'm glad to hear the 1000 cycle internal batteries are doing much, much better.
edit: mandatory bitching about people who put Apple on a pedestal - AppleCare only covers the battery up to 1000 cycles. Mine was at 1080 cycles. Time to open the wallet.