only 3 possibles.
1. extremely high humidity or heat (unlikely Im assuming).
2. Defective pack cell in the battery assy. (which wouldn't be the case if it JUST started happening)
3, Youve been abusing the chemistry of the battery and now its a bit on the 'tortured' side lets say..........
1. did you often drain the battery very low?
2. did you often /always have your macbook on charge,......or did you often / always BOTH have your macbook on charge AND in sleep mode?
1 or 2 are harsh on the battery chemistry and therefore its longevity
all batteries are consumables meant to replaced either in their own "due time" or early due to abuse / misuse.
Your Macbook is under warranty so make an appt and fill them in on all the specifics.
as to final determination thats up to Apple Inc. and nobody here can or should tell you anything definite on final decision.
especially since nobody here can on-hand diagnose your hardware.
Make an appt. with your local shop.
Thanks for your input, PV.
I called Apple & seeked their advice b4 making an appt with Repair.
One agent suggested i do an SMC reset (which i did) and another agent said my situation was normal.
I'll monitor the situation. If other ppl have experiences like mine, i would like to hear from you, thanks.