If so, then this post it for you. Also remember, these settings should also work in both Unity desktop and Gnome classic because Unity (the desktop with a left side panel and stuff :D) also inherit a lot of Gnome classic desktop's functions and applications. For instance, it still uses Nautilus as the file manager, etc.
Anyhow, to access these power management settings, simply click on the right-edge of your screen (as in the below screenshot) and from the menu choose "System Settings".
From the "control center" window, click on "Hardware" to your left and then from your right-side click on "Power Management" which should open a new window as shown in below screenshots.
|4: Here it is...|
For instance, by default every time you close the lid of your Laptop Ubuntu will put it to suspend (stand-by mode) but my Laptop due to few issues fails to "wake up" afterward!.
If this is the case with you too, then you SHOULD disable it (of course, I know that Gayan! :D) by clicking on the drop-down menu right-next to that which says
"When laptop lid is closed" (as in below screenshot). My choice is "Blank screen".
As you can see, you can also change other settings such as "Spin down" your hard disks (if possible) which helps to save some of that batty life, set screen brightness, dim display when "idle" + a few other options once you click on the "General" tab (in the below screenshot).
If you have questions, just throw in some comments and I'll do my best to answer them :). Goo luck.