I have a mid-2009 MBP and the battery health is all over the place. I have been calibrating my battery regularly but it doesn't fix anything. Just typing this post I have seen the health go from 79% to 72%. What is going on?
It is perfectly normal if your battery health (maximum capacity) is more or less than 100%, even when brand new, or if it fluctuates up or down over time. For further details, read the CHECKING STATUS AND HEALTH section of the following link. This should answer most, if not all, of your battery/charging questions:
The built-in batteries in the newer Mac unibody notebooks come pre-calibrated and
do not require regular calibration like the removable batteries in older Apple notebooks.
Will Apple replace the battery for free if it says service battery? The other day I was getting service battery, but after resetting the SMC I'm back to normal.
Batteries are only covered by warranty or AppleCare if they're determined to be defective. Your battery is designed to retain up to 80% of its health for up to 1000 cycles. Since you're below that, you should take your Mac in and let Apple check it out. Barring any manufacturing defects, since batteries are consumable items, is the users' responsibility to replace them when they have depleted.
The "Service Battery" indicator comes on when the battery health drops below 80%, or when there is a problem with the battery.