Apple will replace a battery that has failed from a factory defect within the first year.
Your 600 cycles is NOT a defect or a failure, and is just normal use, and, by itself, not a reason to replace the battery.
If the battery will no longer charge to 80% capacity before the first year of use, Apple should consider that a device failure, and should replace it within warranty. After the first year, Apple calls that an exhausted battery, not a factory fault or failure.
Even if you have the extended AppleCare, batteries are 12 months warranty.
Apple has relaxed that rule somewhat, in my experience, and sometimes will replace at no charge, when you take to an Apple store, and have a "genius" look at it.
Things like swelling batteries, or obvious physical failure might be replaced free, but not a guaranteed result.
The battery has a design lifetime of 1000 charge cycles, failure after that 1000 cycles is definitely a normal fail (and you purchase a replacement). Failure to hold an adequate charge before 1000 cycles, and more than the first 12 months of ownership would mean taking to a "genius", who may decided to replace on the spot - or not. Depends on the day of the week, and who you talk to...
