diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java b/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java
index 6ce631fad9fdd..ae1da56973214 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java
@@ -55,6 +55,7 @@ import android.app.NotificationManager;
 import android.app.PendingIntent;
 import android.app.StatusBarManager;
 import android.app.TaskStackBuilder;
+import android.app.UiModeManager;
 import android.app.WallpaperColors;
 import android.app.WallpaperInfo;
 import android.app.WallpaperManager;
@@ -329,6 +330,12 @@ public class StatusBar extends SystemUI implements DemoMode,
     /** If true, the lockscreen will show a distinct wallpaper */
     private static final boolean ENABLE_LOCKSCREEN_WALLPAPER = true;
 
+    /** Whether to force dark theme if Configuration.UI_MODE_NIGHT_YES. */
+    private static final boolean DARK_THEME_IN_NIGHT_MODE = true;
+
+    /** Whether to switch the device into night mode in battery saver. */
+    private static final boolean NIGHT_MODE_IN_BATTERY_SAVER = true;
+
     /**
      * Never let the alpha become zero for surfaces that draw with SRC - otherwise the RenderNode
      * won't draw anything and uninitialized memory will show through
@@ -941,6 +948,10 @@ public class StatusBar extends SystemUI implements DemoMode,
                 if (mDozeServiceHost != null) {
                     mDozeServiceHost.firePowerSaveChanged(isPowerSave);
                 }
+                if (NIGHT_MODE_IN_BATTERY_SAVER) {
+                    mContext.getSystemService(UiModeManager.class).setNightMode(
+                        isPowerSave ? UiModeManager.MODE_NIGHT_YES : UiModeManager.MODE_NIGHT_NO);
+                }
             }
 
             @Override
@@ -3138,6 +3149,7 @@ public class StatusBar extends SystemUI implements DemoMode,
     public void onConfigChanged(Configuration newConfig) {
         updateResources();
         updateDisplaySize(); // populates mDisplayMetrics
+        updateTheme();
 
         if (DEBUG) {
             Log.v(TAG, "configuration changed: " + mContext.getResources().getConfiguration());
@@ -3878,8 +3890,13 @@ public class StatusBar extends SystemUI implements DemoMode,
         // The system wallpaper defines if QS should be light or dark.
         WallpaperColors systemColors = mColorExtractor
                 .getWallpaperColors(WallpaperManager.FLAG_SYSTEM);
-        final boolean useDarkTheme = systemColors != null
+        final boolean wallpaperWantsDarkTheme = systemColors != null
                 && (systemColors.getColorHints() & WallpaperColors.HINT_SUPPORTS_DARK_THEME) != 0;
+        final Configuration config = mContext.getResources().getConfiguration();
+        final boolean nightModeWantsDarkTheme = DARK_THEME_IN_NIGHT_MODE
+                && (config.uiMode & Configuration.UI_MODE_NIGHT_MASK)
+                    == Configuration.UI_MODE_NIGHT_YES;
+        final boolean useDarkTheme = wallpaperWantsDarkTheme || nightModeWantsDarkTheme;
         if (isUsingDarkTheme() != useDarkTheme) {
             mUiOffloadThread.submit(() -> {
                 try {