Which model of Macintosh has the longest battery life?
According to Apple's website, the 13" MacBook Air and all of the MacBook Pros have 7 hours of battery life. This means that there are seven laptops for you to choose from: Four 13" computers, two 15", and one 17". The possibility of getting more than 7 hours exists, because this number is determined in this manner:


  The wireless web test measures battery life by wirelessly browsing 25 popular websites with display brightness set to 50%.


—Apple (at the very bottom of the page, point number 2).