Hi there! My first post on the site

I am completely new to Android and smartphones in general. I got a Sony Xperia go yesterday, and so far it seems pretty cool. I upgraded to ICS 4.0 and installed the Nova Launcher.
Anyway, this is the thing:
When I have my phone connected to my computer or another power source it becomes considerably smoother than when it is not connected. The thing that bothers me here is that it shows that it is capable of being smooth, but somehow "under-performs" when it is unconnected.
Is there any way I can change this? Some box I need to tick somewhere? Something else I could do? Any tips or hints are very much appreciated

Thank you in advance!