My battery was dead and my laptop got really slow over the time.
The repair was very easy. I had some trouble with the battery screws, one got mangled and I had to remove it with pliers. All in all it took only about 20 minutes.
Upgrading the hard drive to a fusion drive and adding some extra ram increased general performance up to 50 percent, its like a new laptop and worth the $400. Quality of tools and parts is top, thank you guys!!