Controlling the battery charging threshold on Asus laptop with Ubuntu 20.04

From kernel 5.4+ there is an ability to control charging of the laptop battery. In the /sys/class/power_supply/BAT0/ are some variables useful for battery monitoring and controlling.

ls /sys/class/power_supply/BAT0/
alarm device@ manufacturer serial_number uevent capacity energy_full model_name status voltage_min_design
capacity_level energy_full_design power/ subsystem@ voltage_now charge_control_end_threshold energy_now power_now technology cycle_count hwmon2/ present type

One of those variables is charge_control_end_threshold, it is just an integer number indicating when to stop charging.

Whith:

cat /sys/class/power_supply/BAT0/charge_control_end_threshold

we can see actual value of treshold.

Simply whit writing into a variable, we can control when charging stops:

echo 70 | sudo tee /sys/class/power_supply/BAT0/charge_control_end_threshold

Whit this command, treshold is set to 70% and charging will stop on 69%.

Just for convenience, I’ve been made this bash script: /usr/bin/tresho

!/bin/bash
echo $1 | sudo tee /sys/class/power_supply/BAT0/charge_control_end_threshold

And now just type on command prompt: tresho 50 or whatever value you want.

Set this variable during system startup, for making it permanent

Create the following systemd service: etc/systemd/system/tresho.service

[Unit]
After=network.service

[Service]
ExecStart=/usr/bin/tresho70.sh

[Install]
WantedBy=default.target

And this bash script: /usr/bin/tresho70.sh

#!/bin/bash
echo '70' | sudo tee /sys/class/power_supply/BAT0/charge_control_end_threshold

Then activate the service:

sudo service tresho start

Alternate solution

For adjusting battery charging threshold on system startup  create the following systemd service:

/etc/systemd/system/battery-charge-threshold.service
[Unit]
Description=Set the battery charge threshold
After=multi-user.target

[Service]
Type=oneshot
ExecStart=/bin/bash -c 'echo 70 > /sys/class/power_supply/BAT0/charge_control_end_threshold'

[Install]
WantedBy=multi-user.target

and then enable it.

Warning: As of systemd 246, activation of this unit may cause to infinite restart of service above.

/etc/systemd/system/battery-charge-threshold.path
[Path]
PathExists=/sys/class/power_supply/BAT0/
Unit=battery-charge-threshold.service

[Install]
WantedBy=multi-user.target

Create this unit file and enable it. The service above should be disabled since the path unit activating it.

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