feat: add battery conservation mode with Waybar toggle

Laptops with charge_control_end_threshold support get a click-to-toggle
on the battery module (80% ↔ 100%). A ♥ icon appears when conservation
is active, hidden when inactive. State persists across reboots via
systemd oneshot service. udev rule grants wheel group write access
so no sudo is needed for toggling.

CLAUDE.md

@@ -7,7 +7,16 @@ Reproduzierbares Arch-Linux-Setup basierend auf archinstall + Post-Install-Autom
 - `config/` — archinstall-Konfiguration (inkl. custom-commands die das Repo nach /opt/moonarch klonen, root-owned)
 - `scripts/` — Post-Install- und Helper-Scripts
 - `packages/` — Paketlisten (offiziell + AUR), getrennt gepflegt
-- `defaults/` — XDG-Configs, Shell-Config, Helper-Binaries, systemd User-Services, greetd/moongreet-Config, Wallpaper
+- `defaults/` — XDG-Configs, Shell-Config, Helper-Binaries, systemd Services, udev-Regeln, greetd/moongreet-Config, Wallpaper
+
+## Battery Conservation Mode
+
+Laptops mit `charge_control_end_threshold`-Support (ThinkPad, Framework, etc.) erhalten einen Waybar-Toggle:
+- Klick auf das Battery-Modul schaltet zwischen 80% und 100% Ladegrenze um
+- Bei aktiver Conservation erscheint ein ♥-Icon neben der Battery-Anzeige
+- Zustand wird in `/var/lib/moonarch/batsaver-threshold` persistiert und beim Boot via systemd-Service wiederhergestellt
+- udev-Regel gibt Gruppe `wheel` Schreibzugriff auf den Threshold (kein sudo nötig)
+- Auf Desktops ohne Battery-Support versteckt sich das Feature komplett
 
 ## Konventionen
 

DECISIONS.md

@@ -1,5 +1,11 @@
 # Decisions
 
+## 2026-04-08 – Battery conservation mode: udev + sysfs + Waybar toggle
+- **Who**: Dominik, ClaudeCode
+- **Why**: Laptops with `charge_control_end_threshold` support benefit from limiting charge to 80% to extend battery lifespan. Needed a user-friendly toggle without requiring sudo.
+- **Tradeoffs**: udev RUN approach for permissions (group wheel gets write access) vs polkit/pkexec (password prompt on every toggle). Chose udev for seamless UX. State persisted in `/var/lib/moonarch/` (system-wide, not per-user) — acceptable since charge threshold is a hardware setting, not a user preference. Fixed 80% threshold instead of configurable — KISS, matches industry standard.
+- **How**: udev rule grants wheel group write on `charge_control_end_threshold`. Toggle script writes sysfs + state file. systemd oneshot service restores on boot. Waybar shows ♥ icon when active, hidden when inactive. Click on battery module toggles.
+
 ## 2026-04-07 – Walker theme: gtk-inherit → moonarch with fixed colors
 - **Who**: Dominik, ClaudeCode
 - **Why**: gtk-inherit theme relied on GTK4 color inheritance which works but doesn't update live when switching GTK themes (Walker service needs restart). Explicit color definitions make the theme self-contained and predictable.

README.md

@@ -131,11 +131,15 @@ defaults/
     moonarch-waybar-cpugov        Waybar module: CPU governor status
     moonarch-waybar-gpustat       Waybar module: GPU utilization
     moonarch-waybar-hidpp         Waybar module: Logitech HID++ device battery
+    moonarch-waybar-batsaver      Waybar module: battery conservation mode indicator
+    moonarch-batsaver-toggle      Toggle battery charge limit (80% ↔ 100%)
 
   shell/zshrc                   Zsh config: prompt, aliases, FZF, completion
   etc/greetd/                   greetd daemon + greeter Niri config
   etc/moongreet/                moongreet configuration
   etc/systemd/user/             Systemd user services (cliphist, kanshi, walker, nautilus)
+  etc/systemd/system/           System service (battery conservation restore on boot)
+  etc/udev/rules.d/             udev rules (battery threshold permissions)
   backgrounds/wallpaper.jpg     Default wallpaper (shared by desktop, greeter, lock screen)
 ```
 

defaults/bin/moonarch-batsaver-toggle

@@ -0,0 +1,28 @@
+#!/usr/bin/bash
+# ABOUTME: Toggles battery conservation mode between 80% and 100% charge limit.
+# ABOUTME: Writes to sysfs (immediate) and state file (persistence across reboots).
+
+THRESHOLD_FILE="/sys/class/power_supply/BAT0/charge_control_end_threshold"
+STATE_DIR="/var/lib/moonarch"
+STATE_FILE="${STATE_DIR}/batsaver-threshold"
+CONSERVATION_LIMIT=80
+
+[[ -f "$THRESHOLD_FILE" ]] || exit 1
+
+CURRENT=$(cat "$THRESHOLD_FILE")
+
+if [[ "$CURRENT" -le "$CONSERVATION_LIMIT" ]]; then
+    NEW=100
+else
+    NEW="$CONSERVATION_LIMIT"
+fi
+
+# Apply immediately
+echo "$NEW" > "$THRESHOLD_FILE" || exit 1
+
+# Persist for next boot
+mkdir -p "$STATE_DIR"
+echo "$NEW" > "$STATE_FILE"
+
+# Signal Waybar to refresh the batsaver module (SIGRTMIN+9)
+pkill -RTMIN+9 waybar

defaults/bin/moonarch-waybar-batsaver

@@ -0,0 +1,19 @@
+#!/usr/bin/bash
+# ABOUTME: Waybar module showing battery conservation mode status.
+# ABOUTME: Outputs heart icon when active (threshold ≤80), empty when inactive.
+
+THRESHOLD_FILE="/sys/class/power_supply/BAT0/charge_control_end_threshold"
+
+# No battery threshold support → no output → Waybar hides module
+[[ -f "$THRESHOLD_FILE" ]] || exit 0
+
+THRESHOLD=$(cat "$THRESHOLD_FILE")
+
+if [[ "$THRESHOLD" -le 80 ]]; then
+    jq --compact-output -n \
+        --arg text "♥" \
+        --arg tooltip "Battery Conservation: ON (limit ${THRESHOLD}%)" \
+        --arg class "on" \
+        '{text: $text, tooltip: $tooltip, class: $class}'
+fi
+# Threshold > 80 → no output → Waybar hides module

defaults/etc/systemd/system/moonarch-batsaver.service

@@ -0,0 +1,15 @@
+# ABOUTME: Restores battery charge threshold from saved state on boot.
+# ABOUTME: Only runs on laptops with threshold support and a saved state file.
+
+[Unit]
+Description=Restore battery conservation mode threshold
+After=sysinit.target
+ConditionPathExists=/sys/class/power_supply/BAT0/charge_control_end_threshold
+ConditionPathExists=/var/lib/moonarch/batsaver-threshold
+
+[Service]
+Type=oneshot
+ExecStart=/bin/sh -c 'cat /var/lib/moonarch/batsaver-threshold > /sys/class/power_supply/BAT0/charge_control_end_threshold'
+
+[Install]
+WantedBy=multi-user.target

defaults/etc/udev/rules.d/90-moonarch-battery.rules

@@ -0,0 +1,4 @@
+# ABOUTME: udev rule granting wheel group write access to battery charge threshold.
+# ABOUTME: Enables unprivileged toggling of conservation mode via moonarch-batsaver-toggle.
+
+SUBSYSTEM=="power_supply", ATTR{type}=="Battery", RUN+="/bin/sh -c 'chgrp wheel /sys%p/charge_control_end_threshold 2>/dev/null; chmod g+w /sys%p/charge_control_end_threshold 2>/dev/null'"

defaults/xdg/waybar/config

@@ -21,7 +21,7 @@
         "bluetooth",
         "group/sound",
         "backlight",
-        "battery",
+        "group/battery",
         "group/indicators"
     ],
     "group/indicators": {
@@ -58,6 +58,13 @@
             "transition-left-to-right": true
         }
     },
+    "group/battery": {
+        "orientation": "inherit",
+        "modules": [
+            "battery",
+            "custom/batsaver"
+        ]
+    },
     "group/sys": {
         "orientation": "inherit",
         "modules": [
@@ -306,13 +313,26 @@
         },
         "format": "{capacity}% {icon}",
         "format-icons": [
-            "",
-            "",
-            "",
-            "",
-            ""
+            "󰂎",
+            "󰁺",
+            "󰁻",
+            "󰁼",
+            "󰁽",
+            "󰁾",
+            "󰁿",
+            "󰂀",
+            "󰂁",
+            "󰂂",
+            "󰁹"
         ],
-        "max-length": 25
+        "max-length": 25,
+        "on-click": "moonarch-batsaver-toggle"
+    },
+    "custom/batsaver": {
+        "exec": "moonarch-waybar-batsaver",
+        "return-type": "json",
+        "interval": 30,
+        "signal": 9
     },
     "bluetooth": {
         // "controller": "controller1", // specify the alias of the controller if there are more than 1 on the system