Fix ZHA battery when readings produce an unknown value (home-assistan…

…t#23854)

* check for unknown readings

* only publish valid readings

* remove unused constant

homeassistant/components/zha/device_entity.py

@@ -142,8 +142,8 @@ async def async_get_latest_battery_reading(self):
         """Get the latest battery reading from channels cache."""
         battery = await self._battery_channel.get_attribute_value(
             'battery_percentage_remaining')
-        if battery is not None:
-            # per zcl specs battery percent is reported at 200% ¯\_(ツ)_/¯
+        # per zcl specs battery percent is reported at 200% ¯\_(ツ)_/¯
+        if battery is not None and battery != -1:
             battery = battery / 2
             battery = int(round(battery))
             self._device_state_attributes['battery_level'] = battery