Macbook Pro discharges battery when turned off

Question

I've had my Macbook Pro 15" for close to a year now (Mid-2010 revision), and this issue has only happened a couple of times, where when after shutting down the machine at night (full shut-down, not sleep), I turn it back on in the morning to find that the battery has been completely discharged. I thought that the first time, which happened some time ago, probably a few months back, had been me accidentally leaving the computer on running a program which drained the battery, but the most recent incident I am fairly certain that the machine was powered down fully before unplugging the power cord and any other attachments for the night.
I was wondering if this has happened to anyone else, and if it is a major problem? I don't have AppleCare, but may consider getting it before my warranty is up if needed (in about a month) to diagnose/fix the problem with the least trouble/cost. Not afraid to open up my machine if the forum members suggest it, but because the problem is impossible for me to replicate, any solutions (baseless or not) may or may not help and I won't be able to confirm it.
Any help is appreciated!
Steve

Answer 1

Battery health is normal, 97-100% when fully charged and discharges normally when under regular use with the power cord unplugged (about 5-6 hours of usage when under moderate load, can sleep for 6-7 hours and only see a 2-4% drop). WIll post info from the system profiler in case it helps.
Battery Information:
  Model Information:
  Serial Number:          -------------------------
  Manufacturer:          SMP
  Device name:          bq20z451
  Pack Lot Code:          0000
  PCB Lot Code:          0000
  Firmware Version:          0201
  Hardware Revision:          000a
  Cell Revision:          0158
  Charge Information:
  Charge remaining (mAh):          6643
  Fully charged:          Yes
  Charging:          No
  Full charge capacity (mAh):          6643
  Health Information:
  Cycle count:          33
  Condition:          Normal
  Battery Installed:          Yes
  Amperage (mA):          0
  Voltage (mV):          12498
System Power Settings:
  AC Power:
  System Sleep Timer (Minutes):          0
  Disk Sleep Timer (Minutes):          10
  Display Sleep Timer (Minutes):          2
  Wake On AC Change:          No
  Wake On Clamshell Open:          Yes
  Wake On LAN:          No
  Current Power Source:          Yes
  Display Sleep Uses Dim:          Yes
  GPUSwitch:          2
  Battery Power:
  System Sleep Timer (Minutes):          3
  Disk Sleep Timer (Minutes):          10
  Display Sleep Timer (Minutes):          2
  Wake On AC Change:          No
  Wake On Clamshell Open:          Yes
  Display Sleep Uses Dim:          Yes
  GPUSwitch:          2
  Reduce Brightness:          Yes
Hardware Configuration:
  UPS Installed:          No
AC Charger Information:
  Connected:          Yes
  ID:          0x0100
  Wattage (W):          85
  Revision:          0x0000
  Family:          0x00ba
  Serial Number:          0x00c4130e
  Charging:          No