Is this normal for macbook pro?

Hi, so I recently bought a macbook pro 15 retina early 2013 model.

 

What I notice is that my battery percent go down pretty quick I never really timed how long it last because I always charge it back up when I hit like 60 or 70%. I did these system rest and mirgration assistant command thing. When I click on battery indicator to check how long it will last, it shows like 8 hours or about 7 hours when it is at 100%. But when I use it, I notice the percents go down really quick. I would occasionally click on indicator to check the remaining time and It would show like 3 hours left and then it would go back up to 5hours and such.

 

Is this normal? Does this happen to other people too?

 

And I am on lastest ios version.

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