Avoid error when battery appears after homekit has started

homeassistant/components/homekit/accessories.py

@@ -99,6 +99,9 @@ def __init__(
         self.entity_id = entity_id
         self.hass = hass
         self.debounce = {}
+        self._char_battery = None
+        self._char_charging = None
+        self._char_low_battery = None
         self.linked_battery_sensor = self.config.get(CONF_LINKED_BATTERY_SENSOR)
         self.linked_battery_charging_sensor = self.config.get(
             CONF_LINKED_BATTERY_CHARGING_SENSOR
@@ -247,6 +250,10 @@ def update_battery(self, battery_level, battery_charging):
 
         Only call this function if self._support_battery_level is True.
         """
+        if not self._char_battery:
+            # Battery appeared after homekit was started
+            return
+
         battery_level = convert_to_float(battery_level)
         if battery_level is not None:
             if self._char_battery.value != battery_level:
@@ -258,7 +265,8 @@ def update_battery(self, battery_level, battery_charging):
                     "%s: Updated battery level to %d", self.entity_id, battery_level
                 )
 
-        if battery_charging is None:
+        # Charging state can appear after homekit was started
+        if battery_charging is None or not self._char_charging:
             return
 
         hk_charging = HK_CHARGING if battery_charging else HK_NOT_CHARGING

tests/components/homekit/test_accessories.py

@@ -363,9 +363,30 @@ async def test_missing_linked_battery_sensor(hass, hk_driver, caplog):
     await hass.async_block_till_done()
 
     assert not acc.linked_battery_sensor
-    assert not hasattr(acc, "_char_battery")
-    assert not hasattr(acc, "_char_low_battery")
-    assert not hasattr(acc, "_char_charging")
+    assert acc._char_battery is None
+    assert acc._char_low_battery is None
+    assert acc._char_charging is None
+
+
+async def test_battery_appears_after_startup(hass, hk_driver, caplog):
+    """Test battery level appears after homekit is started."""
+    entity_id = "homekit.accessory"
+    hass.states.async_set(entity_id, None, {})
+    await hass.async_block_till_done()
+
+    acc = HomeAccessory(
+        hass, hk_driver, "Accessory without battery", entity_id, 2, None
+    )
+    acc.update_state = lambda x: None
+    assert acc._char_battery is None
+
+    await acc.run_handler()
+    await hass.async_block_till_done()
+    assert acc._char_battery is None
+
+    hass.states.async_set(entity_id, None, {ATTR_BATTERY_LEVEL: 15})
+    await hass.async_block_till_done()
+    assert acc._char_battery is None
 
 
 async def test_call_service(hass, hk_driver, events):