So the late 2008/early 2009 model 15" MBP is rated at holding 5 hours on a single charge. Mine holds 3-4 if I dim my screen way down. I was wondering if anyone has upgraded their battery to a new 2010 model because they now have a rating of 7 hours. Any insight would be great. I'm getting frustrated not knowing exactly how long it's going to last... until I see it plummet down. Thanks.