My 2012 Macbook Pro Retina 15" gets approximately 3.5 to 4.5 hours of battery life with primarily web use. The original battery life was rated up to 7 hours. However I've never achieved 7 hours of web browsing. Currently my battery is at 649 cycles with 79% (6751mah) of the original capacity of 8,460mah. When I got the Macbook Pro it came with Lion which I've upgraded every year to the newest OS but though the performance has gotten a little better I've never achieved the 7hrs as mentioned. I'm wondering now on Yosemite if I purchase a new battery if I will get 7 hours of web browsing assuming i don't watch a lot of videos. I know it depends on a lot of variables. I use to get around 5.5 hrs on the original battery. Correct me if I'm wrong but if I do the math correct depending on my usage I should only see 6 hours at best if I replace the battery.