diff --git a/include/devices.h b/include/devices.h
index fb7d813..3c7ad82 100644
--- a/include/devices.h
+++ b/include/devices.h
@@ -12,8 +12,7 @@ auto roomSensor = Builder<TemperatureSensor>::instance(TEMP_SENSOR)
         .withArea("Basement")
         .withParent(gatewayDevice))
     .withValueTemplate("{{ value_json.sensor.temperature }}")
-    .addDiagnostic(createVoltageSensor(TEMP_SENSOR))
-    .addDiagnostic(createBatterySensor(TEMP_SENSOR, 2.5, 4.5))
+    .addPreconfigured(batterySensors<TemperatureSensor>(TEMP_SENSOR, 2.5, 4.5))
     .build();
 
 auto tankSensor = Builder<Sensor>::instance(new Sensor{ "Level", OIL_SENSOR })
@@ -35,8 +34,7 @@ auto tankSensor = Builder<Sensor>::instance(new Sensor{ "Level", OIL_SENSOR })
         .withValueTemplate("{{ value_json.sensor.value }}")
         .build()
     )
-    .addDiagnostic(createVoltageSensor(OIL_SENSOR))
-    .addDiagnostic(createBatterySensor(OIL_SENSOR, 4.0, 6.4))
+    .addPreconfigured(batterySensors<Sensor>(OIL_SENSOR, 4.0, 6.4))
     .build();
 
 auto presenceTracker = Builder<BinarySensor>::instance(PRESENCE_SENSOR)
@@ -46,8 +44,7 @@ auto presenceTracker = Builder<BinarySensor>::instance(PRESENCE_SENSOR)
         .withModel("AtTiny85")
         .withParent(gatewayDevice))
     .withValueTemplate("{{ value_json.sensor.state }}")
-    .addDiagnostic(createVoltageSensor(PRESENCE_SENSOR))
-    .addDiagnostic(createBatterySensor(PRESENCE_SENSOR, 2.7, 3.3))
+    .addPreconfigured(batterySensors<BinarySensor>(PRESENCE_SENSOR, 2.7, 3.3))
     .withOffDelaySeconds(5*60)
     .withDeviceClass("presence")
     .build();
diff --git a/include/rc_devices.h b/include/rc_devices.h
index ebd37d0..1b33534 100644
--- a/include/rc_devices.h
+++ b/include/rc_devices.h
@@ -77,7 +77,15 @@ VoltageSensor* createVoltageSensor(const char* id) {
 }
 
 BatterySensor* createBatterySensor(const char* id, float min, float max) {
-    char value_json[128];
-    snprintf(value_json, 128, "{{ ((value_json.sensor.diagnostic.voltage|float-%f)|round(2)*100/%f)|int }}", min, max - min);
+    char* value_json = new char[128];
+    snprintf(value_json, 128, "{{ ((value_json.sensor.diagnostic.voltage|float-%.2f)|round(2)*100/%.2f)|int }}", min, max - min);
     return new BatterySensor{id, "Battery level", value_json};
 }
+
+template <class T>
+auto batterySensors(const char* id, float min, float max) {
+    return [id, min, max](Builder<T>& builder) -> Builder<T>& {
+        builder.addDiagnostic(createVoltageSensor(id)).addDiagnostic(createBatterySensor(id, min, max)).build();
+        return builder;
+    };
+}
diff --git a/platformio.ini b/platformio.ini
index f7fb245..8dbfee6 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -33,7 +33,7 @@ framework = arduino
 lib_deps = 
 	${env.lib_deps}
 	arkhipenko/TaskScheduler@^3.8.5
-	https://git.hodos.ro/libraries/ha-mqtt.git@^1.12.0
+	https://git.hodos.ro/libraries/ha-mqtt.git@^1.13.0
 	https://git.hodos.ro/libraries/wifi.git@^2.0.0
 	esphome/ESPAsyncWebServer-esphome@^3.4.0
 upload_port = 192.168.6.161