Add Nuki battery percentage sensor

.coveragerc

@@ -870,6 +870,7 @@ omit =
     homeassistant/components/nuki/binary_sensor.py
     homeassistant/components/nuki/const.py
     homeassistant/components/nuki/lock.py
+    homeassistant/components/nuki/sensor.py
     homeassistant/components/nut/diagnostics.py
     homeassistant/components/nx584/alarm_control_panel.py
     homeassistant/components/nzbget/coordinator.py

homeassistant/components/nuki/__init__.py

@@ -33,7 +33,7 @@
 
 _LOGGER = logging.getLogger(__name__)
 
-PLATFORMS = [Platform.BINARY_SENSOR, Platform.LOCK]
+PLATFORMS = [Platform.BINARY_SENSOR, Platform.LOCK, Platform.SENSOR]
 UPDATE_INTERVAL = timedelta(seconds=30)
 
 

homeassistant/components/nuki/sensor.py

@@ -0,0 +1,52 @@
+"""Battery sensor for the Nuki Lock."""
+
+from homeassistant.components.sensor import SensorDeviceClass, SensorEntity
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.const import PERCENTAGE
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers.entity import EntityCategory
+from homeassistant.helpers.entity_platform import AddEntitiesCallback
+
+from . import NukiEntity
+from .const import ATTR_NUKI_ID, DATA_COORDINATOR, DATA_LOCKS, DOMAIN as NUKI_DOMAIN
+
+
+async def async_setup_entry(
+    hass: HomeAssistant, entry: ConfigEntry, async_add_entities: AddEntitiesCallback
+) -> None:
+    """Set up the Nuki lock sensor."""
+    data = hass.data[NUKI_DOMAIN][entry.entry_id]
+    coordinator = data[DATA_COORDINATOR]
+
+    async_add_entities(
+        [NukiBatterySensor(coordinator, lock) for lock in data[DATA_LOCKS]]
+    )
+
+
+class NukiBatterySensor(NukiEntity, SensorEntity):
+    """Representation of a Nuki Lock Battery sensor."""
+
+    _attr_has_entity_name = True
+
+    _attr_name = "Battery"
+    _attr_native_unit_of_measurement = PERCENTAGE
+    _attr_device_class = SensorDeviceClass.BATTERY
+    _attr_entity_category = EntityCategory.DIAGNOSTIC
+
+    @property
+    def unique_id(self) -> str:
+        """Return a unique ID."""
+        return f"{self._nuki_device.nuki_id}_battery_level"
+
+    @property
+    def extra_state_attributes(self):
+        """Return the device specific state attributes."""
+        data = {
+            ATTR_NUKI_ID: self._nuki_device.nuki_id,
+        }
+        return data
+
+    @property
+    def native_value(self) -> float:
+        """Return the state of the sensor."""
+        return self._nuki_device.battery_charge