If you are running on battery and want to tune your OS to minimise the battery discharge rate to improve battery life then use acpitool with the -B switch:
acpitool -B
 Battery #1     : present
   Remaining capacity : unknown, 32.00%, 00:00:00
   Design capacity    : 5900 mA
   Last full capacity : 5300 mA, 89.83% of design capacity
   Capacity loss      : 10.17%
   Present rate       : 1278 mA <-- MINIMISE THIS NUMBER !!!
   Charging state     : Discharging
   Battery type       : Li-ion