How long does your Macbook Pro MD101 battery last on sleep mode or standby mode?

Hi I'm a newbie to Mac. 🙂just had my MD101 a couple of months ago. I was just wondering because I some some reviews online that the Macbook Pro Md101 or mostly all macbook can have a battery life on standby or sleep mode for 30 days or less. I tried to put my Mac on standby or sleep mode by closing the lid down sometimes and when I opened it for about 4 days it died of from 100 %. For some instaces when I go to sleep I just put the lid down and my battery drains like 8% for 8 hours on sleep.Im just wondering if this is normal. Currently Im on OSX 10.8.3 and I dont have the power sleep activated. Hoping for your kind replies or feedbacks. Thanks🙂