Setting Charge Level Threshold in Lenovo Laptops

Looking at /sys/class/power_supply/BAT0/capacity_level, I see that the capacity is stored in 0-100 percentage values. This makes things easier.

What we need to modify are the following:

1. Set when to stop charging: /sys/class/power_supply/BAT0/charge_stop_threshold
2. Set until when the battery should start charging when plugged in: /sys/class/power_supply/BAT0/charge_start_threshold

The charge_start_threshold used to confuse me. So a table would help.

Assume that charge_start_threshold is 50, and charge_stop_threshold is 100.

The key one is the last two rows, if the battery level is above the charge_stop_threshold and is unplugged, it would not charge the battery. But If the batter was already charging and hit the charge_start_threshold, it would continue to charge until charge_stop_threshold is met.

I also noticed that when the charge_start_threshold needs to be changed, the kernel would not allow setting it above charge_stop_threshold. The reverse is also true.

Keeping it all in mind, I will set three battery profiles.

Like all my other utility scripts, this will also use fzf.

Selecting profile

profile=$(printf 'Home\t45%%\t50%%\nAway\t75%%\t80%%\nFull\t95%%\t100%%' | fzf --height=6 --header="$(printf 'Type\tStart\tMax')" --layout=reverse --prompt='Charge level > ' | cut -f1)

This gives me a tabular view of the profiles and charge level in case I forget the values.

Functions to set charge levels

set_start() {
    echo "${1}" | sudo tee /sys/class/power_supply/BAT0/charge_start_threshold >/dev/null
}
set_stop() {
    echo "${1}" | sudo tee /sys/class/power_supply/BAT0/charge_stop_threshold >/dev/null
}

Now that I am looking at this, I probably should remove sudo dependency from the script. But I use it excessively in my daily life, feel free to remove it or replace it with other tools.

Set charge level based on selected profile

if [ "${profile}" = "Home" ]; then
    set_start 45
    set_stop 50
elif [ "${profile}" = "Away" ]; then
    start=$(head -n 1 /sys/class/power_supply/BAT0/charge_start_threshold)
    # Handle charge level conflict
    if [ "${start}" -gt 75 ]; then
        set_stop 80
        set_start 75
    else
        set_start 75
        set_stop 80
    fi
elif [ "${profile}" = "Full" ]; then
    set_stop 100
    set_start 95
else
    exit 137
fi

The complete script

Combine them all, and ensure POSIX compatibility.

#!/usr/bin/env sh
profile=$(printf 'Home\t45%%\t50%%\nAway\t75%%\t80%%\nFull\t95%%\t100%%' | fzf --height=6 --header="$(printf 'Type\tStart\tMax')" --layout=reverse --prompt='Charge level > ' | cut -f1)
set_start() {
    echo "${1}" | sudo tee /sys/class/power_supply/BAT0/charge_start_threshold >/dev/null
}
set_stop() {
    echo "${1}" | sudo tee /sys/class/power_supply/BAT0/charge_stop_threshold >/dev/null
}
if [ "${profile}" = "Home" ]; then
    set_start 45
    set_stop 50
elif [ "${profile}" = "Away" ]; then
    start=$(head -n 1 /sys/class/power_supply/BAT0/charge_start_threshold)
    if [ "${start}" -gt 75 ]; then
        set_stop 80
        set_start 75
    else
        set_start 75
        set_stop 80
    fi
elif [ "${profile}" = "Full" ]; then
    set_stop 100
    set_start 95
else
    exit 137
fi