It is an extended battery (still on the OG batter). For about the first year it lasted about 5 hours. This was my graduation gift and my mom's real techy so she souped it up pretty nice for me ~$2,200. I'm pretty careful about it too. I don't just let it sit with the plug in,as that kills battery life. I'll go from a full charge all the way down to 0 batter every couple weeks. I'm definitely no computer tech but I'm definitely aware responsible for this computer being as nice as it is. I also download a ton of movies, but I'm definitely careful about what I download.
This is why I'm a firm believe in building your own laptops (i.e. not just going to best buy and buying one off the counter). I know this computer cost quite a bit, but to think that I've had it for this long, and don't really see a reason why I can't continue using it for 2-3 more years, really makes me like Windows-based computers more than osx. Down the line, I might end up buying a new extended batter, but that would just be one part that would cost a couple hundred dollars, unlike an Apple product where you have to get the whole goddamn computer replaced if something goes wrong.
I definitely think Mac's are awesome computers for the right person, don't get me wrong. But for the same amount of money you can build your own PC (not physically, but online) that lasts longer and performs better for equal or lesser price.