Overview

On many laptop’s KDE’s charge-limit slider is only a frontend, and the settings are reset after reboot. Because, the firmware/kernel does not persist it reliably. The usual fix is to apply the limit at boot with a persistent rule or service, instead of relying on KDE Plasma alone.

Good Approach

Writing a systemd service is a standard and reasonable workaround when the KDE setting does not survice the reboot on your hardware. It’s not the most elegant solution, but it gets the job done and it’s a common Linux way to reapply a battery threshold at boot.

Solution

Create a system service file named battery-charge-limit.service in /etc/systemd/system. That is the normal location for custom systemd unit files, while the vendor provided units usually live under /usr/lib/systemd/system or something similar.

Verify Battery Location and Threshold

Check your actual battery path first, because some laptops use a different battery name or different thresholds.

find /sys/class/power_supply/BAT1 -type f | grep -E "charge_control_(start|end)_threshold"

Note: BAT1 maybe be different in your machine

  1. Head inside /etc/systemd/system
cd /etc/systemd/system
  1. Create a file named battery-charge-limit.service
sudo touch battery-charge-limit.service
  1. Open the .service with choice of your editor:
$EDITOR battery-charge-limit.service
  1. Add these lines
[Unit]
Description=Set battery charge limit to 80%
ConditionPathExists=/sys/class/power_supply/BAT1/charge_control_end_threshold

[Service]
Type=oneshot
ExecStart=/bin/bash -c 'echo 80 > /sys/class/power_supply/BAT1/charge_control_end_threshold'

[Install]
WantedBy=multi-user.target

This example assumes your battery is BAT1 and the threshold file is charge_control_end_threshold, which is common but not universal.

Apply the Changes

After saving the file, reload systemd so it notices the new unit, then enable it so it runs automatically at boot:

#reloads the units to detect new file
sudo systemctl daemon-reload

#always starts at boot
sudo systemctl enable --now battery-charge-limit.service