Battstat is a battery status applet that monitors the battery charge level on a laptop. It displays different icons depending on the state of the power subsystem, and will warn if the power drops below a user configurable level. It uses the standard GNOME event system to play user configurable samples at certain events. It's available in binary form for Red Hat (.rpm), Debian (.deb) and FreeBSD (.tgz). You can also compile it yourself by downloading the source tarball (.tar.gz).