New MacBook Air 13´´ - battery drains really fast
So I bought yesterday MacBook Air 13´´. I assumed it was going to be fully or half charged but the battery was dead when I opened the computer. Then I put it on charge and it took about 2-3 hours to fully charge it. After that the battery started to drain really fast, and I didn't expect that. I supposed MacBook 13´´has a battery which could last for about 13 hours, but this is to strange. I don´t have experience with Mac, this is my first Mac, so any suggestions would be appreciated.
P.S. I updated OS X cause App Store said there's an available update. Don´t know if that has anything to do with it.