fdpowermon is a simple perl script that installs an icon in a system
 tray compatible with the freedesktop.org specification.
 .
 Every three seconds, fdpowermon calls acpi to find out what the current
 battery level is. It will set the output of the acpi command as a
 tooltip text, and will update the used icon as appropriate.
 .
 In addition, fdpowermon can optionally call perl subroutines when the
 power reaches a given level. No such subroutines are provided or
 enabled by default, however.