UPower & Power Profiles

The Problem

A shell needs to display battery percentage, charge state, remaining time, and allow switching power profiles (performance / balanced / power-saver). Reading /sys/class/power_supply directly works but requires polling and parsing sysfs files, and power-profiles-daemon uses D-Bus.

The Naive Approach

Reading cat /sys/class/power_supply/BAT0/capacity in a Timer every 5 seconds. This ignores power-supply hotplug, doesn't give charge/discharge rate, and offers no power profile control.

💡Mental Model

UPower is a system-level D-Bus service (org.freedesktop.UPower) that aggregates all power supplies. It emits PropertiesChanged when capacity, state, or time-to-empty changes. Power profiles are managed by net.hadess.PowerProfiles on D-Bus. Both are push-based — subscribe and forget.

The Idea

Use Quickshell's Battery widget (Part IV) for the basics, then extend with the Upower D-Bus service directly for advanced metrics. Add a power profile toggle using powerprofilesctl or direct D-Bus calls via Process.

Let's Build It

import Quickshell
import Quickshell.Widgets

Row {
  spacing: 6

  Battery {
    id: battery
    visible: battery.available
  }

  // Power profile switcher
  Button {
    text: "Power Saver"
    onClicked: {
      Process.exec("powerprofilesctl set power-saver")
    }
  }

  Button {
    text: "Balanced"
    onClicked: {
      Process.exec("powerprofilesctl set balanced")
    }
  }

  Button {
    text: "Performance"
    onClicked: {
      Process.exec("powerprofilesctl set performance")
    }
  }
}

🛠️Let's Build It

The Battery widget handles UPower D-Bus integration internally — it binds to Battery.percentage, Battery.charging, and Battery.timeRemaining. For power profiles, we shell out to powerprofilesctl. A more robust version would call D-Bus directly via Process with gdbus or busctl.

Let's Improve It

Read the current active profile on startup and highlight the active button. Poll powerprofilesctl get at startup and cache it. For a fully reactive approach, subscribe to net.hadess.PowerProfiles PropertiesChanged over D-Bus.

property string activeProfile: "balanced"

Component.onCompleted: {
  Process.run("powerprofilesctl get").stdout.then(out => {
    activeProfile = out.trim()
  })
}

⚠️Common Mistake

Assuming all devices have a battery. Always check Battery.available before showing battery UI. Some desktops (desktops, servers) lack batteries entirely. Also check that powerprofilesctl exists before showing the profile switcher.

Under the Hood

UPower exposes org.freedesktop.UPower.Device on each battery. Properties include Percentage, State (charging/discharging/full), TimeToEmpty, EnergyRate. Quickshell's Battery widget subscribes to PropertiesChanged on all matching devices. Power profiles use net.hadess.PowerProfiles which has ActiveProfile and Profiles properties.

Exercises

Beginner: Display battery icon that changes based on charge level (0-25%, 25-50%, etc.) and charging state.

Intermediate: Build a power profile popup that shows performance mode descriptions and shows which profile is active.

Advanced: Create a power-saving mode that dims the screen, reduces animation framerate, and pauses non-essential timers when on battery below 20%.

✅What You've Learned

• UPower and power-profiles-daemon give your shell battery state and performance control
• Quickshell Battery widget wraps UPower for charge and status
• Power profiles (performance/balanced/power-saver) require direct D-Bus or powerprofilesctl