What OS did it come with? I'd stick with that one if it is Windows 7 or above. With newer versions of Windows, you can always adjust the power-performance ratio by adjusting the power profile settings. Dim the screen, set the CPU to the lowest minimum and highest maximum and make it sleep or hibernate frequently and as soon as it is idle. some things might be annoying, but it will maximize battery life while keeping the processor running at full speed only when you need it.
it has win8, i was thinking that Ubuntu would be much lighter for a notebook with light tasks
The laptop was designed to run under Windows so it will run best with Windows 8. The best way to find out, though, is to do a dual install. You can install Ubuntu side by side with Win 8 and see which one runs faster, cooler, quieter and longer.
Ok, that's what im gonna do, any recommended distribution of Linux ?