diff --git a/src/main.cpp b/src/main.cpp
index 21f9f19..c49747d 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -14,6 +14,8 @@
 #define MQTT_MANUFACTURER "Baumann Enkataleiptics"
 #define AUTH_USERNAME "admin"
 #define MQTT_PROBE_TIMEOUT_MS 400  // keep short: blocks loop()/handleClient() per reconnect attempt
+#define MQTT_PAYLOAD_AVAILABLE "online"
+#define MQTT_PAYLOAD_NOT_AVAILABLE "offline"
 
 struct MeterConfig {
   int pin;
@@ -256,6 +258,9 @@ static void mqttPublishDiscovery() {
     doc["name"]              = name;
     doc["state_topic"]       = stat;
     doc["command_topic"]     = stat + "/set";
+    doc["availability_topic"]    = String(mqttCfg.prefix) + "/status";
+    doc["payload_available"]     = MQTT_PAYLOAD_AVAILABLE;
+    doc["payload_not_available"] = MQTT_PAYLOAD_NOT_AVAILABLE;
     doc["min"]               = meters[i].rangeMin;
     doc["max"]               = meters[i].rangeMax;
     doc["step"]              = 0.1;
@@ -268,7 +273,7 @@ static void mqttPublishDiscovery() {
 
     char topic[128];
     snprintf(topic, sizeof(topic), "homeassistant/number/%s/config", objId.c_str());
-    char payload[512];
+    char payload[768];
     serializeJson(doc, payload, sizeof(payload));
     bool pubOk = mqttClient.publish(topic, payload, true);
     Serial.printf("[MQTT] discovery %s -> %s (ok=%d)\n", topic, payload, pubOk);
@@ -323,11 +328,11 @@ static bool mqttConnect() {
 
   Serial.printf("[MQTT] connecting to %s:%d as %s\n", mqttCfg.host, mqttCfg.port, clientId);
   bool ok = mqttClient.connect(clientId, user, pass,
-                               statusTopic, 0, true, "online: false");
+                               statusTopic, 0, true, MQTT_PAYLOAD_NOT_AVAILABLE);
 
   if (ok) {
     Serial.printf("[MQTT] connected to %s:%d\n", mqttCfg.host, mqttCfg.port);
-    mqttClient.publish(statusTopic, "online: true", true);
+    mqttClient.publish(statusTopic, MQTT_PAYLOAD_AVAILABLE, true);
     mqttSubscribe();
     mqttPublishDiscovery();
     for (int i = 0; i < meterCount; i++)