MacBook pro retina battery problem, how to fix this?

I'm using my Macbook Pro Retina (2.7 GHz i7 | 16GB DDR3 | 768 SSD) since the first week of july. It just had 7 battery cycles, condition is normal.

Since yesterday I found out my battery percentage dropped from somewhere between 70-80% to 35% directly after I opened up my macbook when I came home (15 minute ride). (I didn't actually see it drop)

I tried the tricks found on the internet such as:

• Open Terminal
• cd ~/Library/Preferences/
  rm com.apple.desktop.plist
  killall Dock

Things I found out:

1. The com.apple.desktop.plist file was missing. So I 'manually' created it by changing the wallpaper, nonsense off course.
2. This didn't help off course because a damaged file could have been the problem, but if there isn't any - it can't be the problem.
3. The killall dock cmd didn't do what it should do - because it said "No matching processes belonging to you were found".
4. I tried to reset SMC, no fix.
5. I tried to restart with cmd + option + p + r, no fix.
6. First week(s) i didn't notice any battery drops or any problem with the battery.

I called the local (Netherlands) Apple support services. I know some about computers and nowdays technology so it's annoying talking to someone which is trying to help me using manuals or so. The guy 3 times called his (smarter on mac) colleague to help him and sort of concluded that it maybe are some App(s) running in the back killing the CPU. I think that's not the problem. Still I monitored it and indeed, it isn't the problem.

The thing I do noticed is that my battery charges up way too fast:

• 8% - 2:01 remaining (real time: 8:15 AM)
• 9% - 1:32 remaining (real time: 8:17 AM)
• 23% - 1:57 remaining (real time: 8:30 AM)
• 27% - 1:18 remaining (real time: 8:34 AM)
• 52% - 0:50 remaining (real time: 9:00 AM)

This is while using only Safari.

I can't imagine that my battery is broken already. Especially since I have used it just for two weeks and everything was fine in the beginning.

Can someone please help me? I rather don't go back to the Apple Store and wait for them to fix it. Especially after my last 3 expierences with them not able to fix my two first generation macbook air's. When I took a try I both fixed them, with just reinstalling the OS.

Thanks in advance!