Battery capacity normally go up and down.
Is it stuck at 87% or less now, or does it go up to over 90% at times?
But when you get it new, your battery should be at 100% capacity, and not 98%.
Was the battery cycle count at 0 when you got it?
Was yours a brand new in sealed-box unit?
Or you bought a used unit?
Or you got it in an opened box (which means it has possibly been used before)?
Apple states that their batteries (beginning with MacBooks released from 2009 and later) maintain at least 80% charge over a period of up to 1000 full charge cycles.
However, this is provided that you use the battery within the expected temperature range, etc.
If you use your MacBook everyday in the sun or perhaps even do heavy gaming with no cooler pad or aircon environment, the capacity will drop way faster due to heat damage as batteries and heat do not go hand in hand.
So if your MacBook is approaching 80% fast before even close to 100 charge cycles, sounds like a defect to me.
But if I were you, I would use it for a little while more to see whether the battery capacity jumps back to over 90%.
This post has been edited by shockk: Sep 8 2012, 02:07 AM