Hi, I just bought my mac 2 weeks ago and I was told the battery would last 6-7 hours. I thought that was a lot and was pretty happy. However, my battery lasts about an hour and a half. And I find myself having to recharge it a lot more than expected. My friends who have had their macs for a few years have batteries that last longer than mine. Any suggestions on what I should do? And any ideas on why this might be?