My macbook pro is suddenly shutting down.

Question

My mac it is aproximately 2 years old, is  suddenly shutting down with any process, it just goes black and a switch saound like if it was forced. It normally happens when the charger isnt connected.
Battery Information:
  Model Information:
  Serial Number:          9G2060A7VD3MA
  Manufacturer:          DP
  Device Name:          bq20z451
  Pack Lot Code:          0
  PCB Lot Code:          0
  Firmware Version:          201
  Hardware Revision:          2
  Cell Revision:          158
  Charge Information:
  Charge Remaining (mAh):          4857
  Fully Charged:          No
  Charging:          Yes
  Full Charge Capacity (mAh):          5425
  Health Information:
  Cycle Count:          342
  Condition:          Normal
  Battery Installed:          Yes
  Amperage (mA):          1386
  Voltage (mV):          12465
System Power Settings:
  AC Power:
  System Sleep Timer (Minutes):          10
  Disk Sleep Timer (Minutes):          10
  Display Sleep Timer (Minutes):          10
  Wake on AC Change:          No
  Wake on Clamshell Open:          Yes
  Wake on LAN:          Yes
  Current Power Source:          Yes
  Display Sleep Uses Dim:          Yes
  PrioritizeNetworkReachabilityOverSleep:          0
  Standby Delay:          4200
  Standby Enabled:          0
  Battery Power:
  System Sleep Timer (Minutes):          10
  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
  Reduce Brightness:          Yes
  Standby Delay:          4200
  Standby Enabled:          0
Hardware Configuration:
  UPS Installed:          No
AC Charger Information:
  Connected:          Yes
  ID:          0x0100
  Wattage (W):          85
  Revision:          0x0000
  Family:          0x0085
  Serial Number:          0x007fddd2
  Charging:          Yes

Answer 1

First reset the SMC http://support.apple.com/kb/HT3964