My mom recently bought me a 13-inch MacBook Pro (Lion) from Best Buy for college and it was a thrill after suffering from pc crashes. Now I have read that Apple claims that these MBPs can last up to 7 hours of wifi use. However, my mac has only calculated after full charging, 4 hours (4:17) of usage. Is there any problem? So I was thinking this: 13-inch will get 4 hours, 15-inche will get 6 hours, and 17-inch will get 7 hours of battery life. HELP me.