Laptop users: powerapplet_tray no longer works in slackware derivatives after kernel 5.9.
qbat is used in ubuntu derivatives, but requires qt4 - minimum 13mb extra for slacks.
The battery percentage remaining is found on my systems via the following terminal command:
cat /sys/class/power_supply/BAT*/capacity
(I found my systems have either BAT0 or BAT1, but as only 1 battery, above will do).
EDIT: newer powerapplet_tray from Slacko64-8.2.1 works ON SOME PCS; .pet several posts down.
EDIT2: slacko derived .pet fails on my machine with BAT0. See discussion further down.
EDIT 3: Have hacked a .pet to run above terminal command, but not releasing yet.