diff --git a/haos-addon/config.yaml b/haos-addon/config.yaml
index b319975..f890ec6 100644
--- a/haos-addon/config.yaml
+++ b/haos-addon/config.yaml
@@ -1,5 +1,5 @@
 name: ShineBridge
-version: "1.8.19"
+version: "1.8.20"
 slug: shinebridge
 description: Growatt Wechselrichter lokal in Home Assistant — Modbus TCP via ShineLAN-X, MQTT Discovery, Web UI
 url: https://gitea.bitfire.work/retr0/shinebridge
diff --git a/haos-addon/src/main.py b/haos-addon/src/main.py
index f597df8..b990f72 100644
--- a/haos-addon/src/main.py
+++ b/haos-addon/src/main.py
@@ -480,22 +480,25 @@ def api_save_config():
                 State.mqtt_cfg[k] = data[k]
         if data.get("mqtt_pass"):
             State.mqtt_cfg["mqtt_pass"] = data["mqtt_pass"]
-        for k in ("price_import", "price_export", "spot_markup"):
-            if k in data:
-                State.mqtt_cfg[k] = float(data[k])
+        for k in ("price_import", "price_export", "spot_markup", "monthly_rate_eur", "grundpreis_eur_per_month"):
+            if k in data and data[k] is not None:
+                try:
+                    State.mqtt_cfg[k] = float(data[k])
+                except (ValueError, TypeError):
+                    pass
         for k in ("billing_day", "billing_month"):
-            if k in data:
-                State.mqtt_cfg[k] = int(data[k])
+            if k in data and data[k] is not None:
+                try:
+                    State.mqtt_cfg[k] = int(data[k])
+                except (ValueError, TypeError):
+                    pass
         for k in ("tariff_type", "spot_country"):
-            if k in data:
+            if k in data and data[k] is not None:
                 State.mqtt_cfg[k] = str(data[k])
         if "spot_chart" in data:
             State.mqtt_cfg["spot_chart"] = bool(data["spot_chart"])
         if "billing_tracker_enabled" in data:
             State.mqtt_cfg["billing_tracker_enabled"] = bool(data["billing_tracker_enabled"])
-        for k in ("monthly_rate_eur", "grundpreis_eur_per_month"):
-            if k in data:
-                State.mqtt_cfg[k] = float(data[k])
         save_config()
     threading.Thread(target=_restart_all, daemon=True).start()
     return jsonify({"ok": True})
@@ -569,8 +572,8 @@ def api_period_energy():
         pv_total = entry.get("total_energy_total")
         grid_exp = entry.get("grid_export_kwh")
         bat_dch  = entry.get("bat_discharge_total")
-        if pv_total is not None and grid_exp is not None:
-            savings = round(max(0.0, pv_total - grid_exp), 2)
+        if pv_total is not None:
+            savings = round(max(0.0, pv_total - (grid_exp or 0.0)), 2)
             entry["savings_kwh"] = savings
             entry["savings_eur"] = round(savings * eff_price, 2)
         elif bat_dch is not None:
diff --git a/haos-addon/src/web/index.html b/haos-addon/src/web/index.html
index 01291e5..4eb41b3 100644
--- a/haos-addon/src/web/index.html
+++ b/haos-addon/src/web/index.html
@@ -1319,8 +1319,8 @@ async function savePrices() {
     spot_markup:   parseFloat(document.getElementById("cfg-spot-markup").value   || 0),
     spot_country:  document.getElementById("cfg-spot-country").value,
     spot_chart:    document.getElementById("cfg-spot-chart").checked,
-    billing_day:   parseInt(document.getElementById("cfg-billing-day").value),
-    billing_month: parseInt(document.getElementById("cfg-billing-month").value),
+    billing_day:   parseInt(document.getElementById("cfg-billing-day").value)   || 1,
+    billing_month: parseInt(document.getElementById("cfg-billing-month").value) || 1,
     billing_tracker_enabled:    document.getElementById("cfg-billing-tracker").checked,
     monthly_rate_eur:           parseFloat(document.getElementById("cfg-monthly-rate").value || 0),
     grundpreis_eur_per_month:   parseFloat(document.getElementById("cfg-grundpreis").value   || 0),