SlackBuildsOrg/system/xbattmon

xbattmon is a simple battery status bar for X. It draws a 2 pixels bar
at the edge of your screen, which shows battery status with different
colors.

You can configure xbattmon at build time by passing the following
variables to the script (VAR=<...> ./xbattmon.SlackBuild):

COLOR_CHARGED=<color> (default: green)
COLOR_LEFT2CHARGE=<color> (default: grey)
COLOR_DRAINED=<color> (default: red)
COLOR_LEFT2DRAIN=<color> (default: blue)
RAISE=yes|no (default: no), the bar to be raised on top of other windows
CRITICAL=<number> (default: 5), the charge level at which starts blinking
TRANSPARENT=yes|no (default: no)