Energy saver 101 : sleeps after or when battery is at x hours? Using Mac OSX on a macbook pro. in energy saver - battery tab : if i have sleep at 1 hour, does that mean the computer will sleep after an hour on battery OR when there is a about an hour of battery remaining?

If its the former -> is there a way to make it the latter? I want the computer to sleep when battery has about half an hour left. 

Can use terminal or preferences or put a well known freeware.
It means the computer will sleep after an hour.
The computer (if it's a laptop) will automatically hibernate when the battery is very low (this is hibernatemode 3). Is that sufficient or do you really want the computer to sleep when there's 1 hour of battery left?