Application to underclock/undervolt a Mac? [closed]

Coolbook will do it, but might have difficulties with newer MBPs. Also, the latest version at least has a $10 license fee.

I would be inclined to think that there would be a Unixy/CLI utility for this, although I don't know one off-hand.

As a start, be sure to set your Energy Saving settings (in the System Preferences) to Save more energy. That should extend battery life some.

There's a kernel extension and a free app for controlling Intel SpeedStep using "sysctl"

http://code.google.com/p/xnu-speedstep/

To see which frequencies are available:

sysctl kern.cputhrottle_freqs

To switch frequency:

sudo sysctl -w kern.cputhrottle_curfreq=YYYY