Shell script to set battery charge limits on Thinkpads with post-2018 kernels (acpi_call kernel module not needed)

limit_charge.sh

#!/bin/bash

# On post-2018 kernels the Thinkpad charge threshold mechanism has
# been included in the thinkpad-acpi module. Hence the tpacpi-bat
# tool (and the acpi_call kernel module) are no longer necessary;
# you can just set the values in sysfs.

# Stop charging at this percentage
STOP_AT=80
# Start charging at this percentage
START_AT=75
# When charging to full capacity, restart at this percentage
START_AT_FULL=95

start_dev=/sys/class/power_supply/BAT0/charge_start_threshold
stop_dev=/sys/class/power_supply/BAT0/charge_stop_threshold

# Do this in a difficult way because the order of settings matters.
# args: start-percent stop-percent
do_set() {
	( echo $1 > $start_dev ) 2> /dev/null
	echo $2 > $stop_dev
	echo $1 > $start_dev
}

case "$1" in
limit)
	do_set $START_AT $STOP_AT
	;;

full)
	do_set $START_AT_FULL 100
	;;

status)
	start=$(cat $start_dev)
	# 0 = function disabled
	[[ $start = 0 ]] && start=100
	stop=$(cat $stop_dev)

	echo "start: $start% stop: $stop%"
	;;
*)
	echo "usage: $0 limit|full|status"
	false
	;;
esac