diff --git a/js/components/error-boundary.js b/js/components/error-boundary.js
index 0efeac9..862754b 100644
--- a/js/components/error-boundary.js
+++ b/js/components/error-boundary.js
@@ -88,6 +88,42 @@ export function setupGlobalErrorHandler() {
         console.error('Unhandled promise rejection:', event.reason)
         showErrorToast(event.reason?.message || 'Ein Fehler ist aufgetreten')
     })
+
+    // Offline/Online detection
+    setupOfflineIndicator()
+}
+
+/**
+ * Shows/hides offline indicator based on network status
+ */
+function setupOfflineIndicator() {
+    const updateStatus = () => {
+        let indicator = document.querySelector('.offline-indicator')
+        
+        if (!navigator.onLine) {
+            if (!indicator) {
+                indicator = document.createElement('div')
+                indicator.className = 'offline-indicator'
+                indicator.innerHTML = `
+                    <span class="offline-icon">📡</span>
+                    <span class="offline-text">Offline</span>
+                `
+                document.body.appendChild(indicator)
+                requestAnimationFrame(() => indicator.classList.add('visible'))
+            }
+        } else {
+            if (indicator) {
+                indicator.classList.remove('visible')
+                setTimeout(() => indicator.remove(), 300)
+            }
+        }
+    }
+
+    window.addEventListener('online', updateStatus)
+    window.addEventListener('offline', updateStatus)
+    
+    // Check on init
+    updateStatus()
 }
 
 /**
@@ -214,6 +250,40 @@ style.textContent = /* css */`
     .error-toast-close:hover {
         color: var(--color-text);
     }
+
+    /* Offline Indicator */
+    .offline-indicator {
+        position: fixed;
+        top: var(--space-md);
+        left: 50%;
+        transform: translateX(-50%) translateY(-100px);
+        display: flex;
+        align-items: center;
+        gap: var(--space-xs);
+        padding: var(--space-xs) var(--space-md);
+        background: var(--color-bg-secondary);
+        border: 1px solid var(--color-border);
+        border-radius: var(--radius-full);
+        box-shadow: var(--shadow-md);
+        z-index: 10001;
+        opacity: 0;
+        transition: transform 0.3s ease, opacity 0.3s ease;
+    }
+
+    .offline-indicator.visible {
+        transform: translateX(-50%) translateY(0);
+        opacity: 1;
+    }
+
+    .offline-indicator .offline-icon {
+        filter: grayscale(1);
+    }
+
+    .offline-indicator .offline-text {
+        font-size: var(--font-size-sm);
+        font-weight: var(--font-weight-medium);
+        color: var(--color-text);
+    }
 `
 document.head.appendChild(style)
 
diff --git a/js/services/currency.js b/js/services/currency.js
index f8c3e91..2c0ba66 100644
--- a/js/services/currency.js
+++ b/js/services/currency.js
@@ -16,8 +16,8 @@ const CURRENCY_SYMBOLS = {
     JPY: '¥'
 }
 
-const CACHE_DURATION = 10 * 60 * 1000 // 10 minutes (CoinGecko free tier: 10-30 req/min)
-const MIN_REQUEST_INTERVAL = 6 * 1000 // 6 seconds between requests (max ~10/min)
+const CACHE_DURATION = 30 * 60 * 1000 // 30 minutes (CoinGecko free tier is strict)
+const MIN_REQUEST_INTERVAL = 60 * 1000 // 60 seconds between requests
 
 let cachedRates = null
 let cacheTimestamp = 0
diff --git a/service-worker.js b/service-worker.js
index 9dedd69..ef96578 100644
--- a/service-worker.js
+++ b/service-worker.js
@@ -1,4 +1,4 @@
-const CACHE_NAME = 'dgray-v27';
+const CACHE_NAME = 'dgray-v28';
 const STATIC_ASSETS = [
     '/',
     '/index.html',
@@ -16,6 +16,8 @@ const STATIC_ASSETS = [
     '/js/components/chat-widget.js',
     '/js/components/listing-card.js',
     '/js/components/search-box.js',
+    '/js/components/error-boundary.js',
+    '/js/services/currency.js',
     '/locales/de.json',
     '/locales/en.json',
     '/locales/fr.json',