The battery is covered if it is defective but not if the problem is just normal wear and tear. Apple recommends that you let the battery discharge completely at least once a month to keep it in best shape. If in the two years you owned the machine you have only done this once or twice, or 600 times, or the battery only charges to 89%, Apple will probably call this normal wear. If, on the other hand, the battery does not charge or discharges rapidly, Apple might say the battery is defective and replace it.
The only way to know for sure is to call Applecare.