PowerManagement

The Power Management is managed by ACPI (Advanced Configuration & Power Interface)

See packages : dpkg -l | grep acpi ii acpi                                 1.6-1                          displays information on ACPI devices ii acpi-fakekey                         0.138-10                       tool to generate fake key events ii acpi-support                         0.138-10                       scripts for handling many ACPI events ii acpi-support-base                    0.138-10                       scripts for handling base ACPI events such as the power button ii acpid                                1:2.0.14-2                     Advanced Configuration and Power Interface event daemon dpkg -l |grep pm-utils ii pm-utils                             1.4.1-9                        utilities and scripts for power management

First search result
http://www.thinkwiki.org/wiki/How_to_make_ACPI_work

http://pm-utils.freedesktop.org/wiki

http://wiki.debian.org/ACPI

http://numpanglewat.wordpress.com/2009/01/15/more-faster-acpi-shutdown-on-debian-change-your-acpi-script/

http://old-en.opensuse.org/Pm-utils

https://github.com/craig/cbatt

More
Monitor you power consumption with powertop : http://www.linuxpowertop.org/ ; http://www.linuxpowertop.org/known.php