Sudden turn off problem in my laptop (Samsung RV518-S01IN ) on battery

HI

My laptop is 4 months old, it is Samsun NP-RV518-S01IN and now I have suddenly started facing this problem on battery mode that it sometimes turns off itself all suddenly without any prior warning. It is not shutting down but just goes off as if someone pulled out the battery and when restart it again works fine. Then again turns off, I am using mostly on AC so its not problem but sometimes when I use on battery.. its big problem.

My laptop has Corei3 second generation, 500 GB hdd, 4 GB RAM and running windows 7

I have now clue where is problem.