I've got a MacBook Pro (revision 5,3) which was produced in the middle of 2009 and has 49 charge cycles. When it was all new, it showed a battery capacity of around 6500 mAh.
Now that I've been using it a few months (regularly on battery), the capacity dropped to 6400 mAh at 49 cycles.
Unfortunately I had have a little issue with the MacBook's sleep mode: it seems that if my battery gets low, I get a warning message, and about 10 minutes later it simply shuts down. What I find weird about this is that it's not entering sleep (until the battery is completely depleted), but it simply shuts down, and when I connect it to mains, it restores from the safe sleep (loads RAM from disk).
I tried resetting PRAM, SMC and also re-calibrated the battery. Any ideas?
The problem I see is the fact that the MacBook does not go to sleep when the battery is empty. My previous MacBooks went to sleep a while after the battery warning, keeping the RAM alive for a few hours before the battery gets completely empty, then shutting down (deep sleep/suspend to disk). During that time you could reconnect the power supply and the MacBook resumed from RAM instead of disk.
When the battery reaches "empty", the computer is forced into sleep mode. The battery actually keeps back a reserve beyond "empty", to maintain the computer in sleep for a period of time. Once the battery is truly exhausted, the computer is forced to shut down. At this point, with the safe sleep function introduced in the PowerBook G4 (15-inch Double-Layer SD) computers, the computer's memory contents have been saved to the hard drive. When power is restored, the computer returns itself to its pre-sleep state using the safe sleep image on the hard drive.
You see, the problem is that my MacBook does not go to sleep, instead is simply shuts down.