I am considering getting a 4GB/256GB refurb, and am just wondering about the battery life on the 2011 with Mountain Lion installed. I understand the battery life in the 2011's originally were nothing to write home about, but since installing Mountain Lion, has it improved. What is everyone getting, on average with normal use? I currently have the 2010, and get around 4.5-5 hours, so I am hoping to be on par with that...