Battery Charging Threshold for Acer laptops on Linux

As an owner of an Acer Nitro 5 (AN515-57), I wanted to extend the lifespan of my battery by limiting its charging capacity to 80%. Unfortunately, Acer doesn't provide an official solution for this on Linux. However, with the power of open-source tools, we can still achieve this functionality.

• acer-wmi-battery: this repository hosts the custom kernel driver providing this functionality. However, it's recommended to use the alternative below while the pull request is still under discussion.

  • acer-wmi-battery with DKMS support: use this one for now. This is a fork with DKMS support: this means that you won't need to re-build the driver again after a kernel update.
  • PR discussion: ongoing discussion regarding the pull request mentioned above.

• Startup application to fix health_mode persistence: a bug makes the health_mode value reset back to 0 every week or so when I turn on my laptop and it disables the feature. The workaround I figured out for now is creating a service that will force the value to be 1 when I log in the machine. See instructions on section below.

  • Alternative: GNOME extension to fix health_mode persistence: it offers a nice GUI and can be helpful if you prefer not to create the service below yourself.

Startup application to fix health_mode persistence

I created this script to enable health mode in /home/brenobaptista/bin/limit-acer-battery.sh:

#!/bin/bash
echo 1 | tee /sys/bus/wmi/drivers/acer-wmi-battery/health_mode

I made my script executable with:

chmod +x limit-acer-battery.sh

Then I created this systemd service to run on startup in /etc/systemd/system/acer-battery.service:

[Unit]
Description=Limit Acer battery service

[Service]
ExecStart=/home/brenobaptista/bin/limit-acer-battery.sh

[Install]
WantedBy=multi-user.target

Optional, for security: grants read and write permissions to the owner and read permissions to the group. Others will have no permissions.

sudo chmod 640 /etc/systemd/system/acer-battery.service

When adding a new unit file or editing an existing one, you must tell systemd to reload the unit file definitions:

sudo systemctl daemon-reload

To start the service:

sudo systemctl start acer-battery

To enable it to run at boot:

sudo systemctl enable acer-battery

We can check the status of this service anytime by running:

systemctl status acer-battery

The default service user is already root, so you don't need to use sudo to launch your scripts on startup.

Uninstallation

In case you want to uninstall the software above, here are the links:

• Uninstallation for acer-wmi-battery with DKMS support

• Uninstallation of the startup application

  • Stop the service by running sudo systemctl stop acer-battery
  • Disable it to run at boot by running sudo systemctl disable acer-battery
  • Delete the files created earlier.

• Uninstallation for GNOME extension

  • Don't forget to remove the polkit rules before uninstalling the extension.

Debugging

A few days after the publishing of this post, a reader called Anhar reported that he had the same laptop model but it didn't work for him. It turned out that a custom fan control driver nbfc-linux was conflicting with the custom battery charging driver. So when debugging, make sure to disable other custom drivers to identify any conflicts.

To check if the service is running, run lsmod | grep -i acer and look for acer_wmi_battery.

To check if the DKMS is working, run dkms status | grep -i acer and look for acer_wmi_battery.

To check if the health_mode is enabled, run: cat /sys/bus/wmi/drivers/acer-wmi-battery/health_mode. If it returns 1, it indicates that health_mode is enabled. However, if it returns 0, you need to manually set it to 1 using an editor. You'll have to do it with sudo.