Extending battery life on X200

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With the changes below and a 9 cell battery I get over 9 hours on an idle system with backlight on but at the lowest level. Before the changes I was getting a bit over 5 hours.

The changes fall in 2 categories:

  • Removing packages that create unnecessarily frequent wake up interrupts.
    • These interrupts wake up the CPU, preventing it from staying in its most energy efficient state.
    • I used Powertop from www.lesswatts.org for this task.
  • Lowering the voltage supplied to the CPU.
    • Lowering the voltage supplied to the CPU has other positive side effects beside battery life: my system runs a lot cooler and ... I do not need tpfan (sw fan control for the ThinkPad), the built-in hw controller does a great job and falls back to lower speed shortly after a CPU load subsides.
    • It should be noted that this does not affect performance since the clock runs at the same speeds (22700, 22600, 16000, or 800Mhz for the X200).
    • I used phc patches and phctools available at www.linux-phc.org for this task.