Copy unit_of_measurement onto energy inverted power sensor

homeassistant/components/energy/sensor.py

@@ -715,6 +715,9 @@ def _update_state(self) -> None:
                 self._attr_native_value = None
                 return
 
+            self._attr_native_unit_of_measurement = source_state.attributes.get(
+                ATTR_UNIT_OF_MEASUREMENT
+            )
             self._attr_native_value = value * -1
 
         elif self._is_combined:
@@ -763,13 +766,11 @@ async def async_added_to_hass(self) -> None:
             # Check first sensor
             if source_entry := entity_reg.async_get(self._source_sensors[0]):
                 device_id = source_entry.device_id
-                # For combined mode, always use Watts because we may have different source units; for inverted mode, copy source unit
+                # Combined mode always emits Watts because we convert
+                # heterogeneous source units internally. For inverted mode the
+                # unit is copied from the source state in _update_state.
                 if self._is_combined:
                     self._attr_native_unit_of_measurement = UnitOfPower.WATT
-                else:
-                    self._attr_native_unit_of_measurement = (
-                        source_entry.unit_of_measurement
-                    )
                 # Get source name from registry
                 source_name = source_entry.name or source_entry.original_name
             # Assign power sensor to same device as source sensor(s)

tests/components/energy/test_sensor.py

@@ -1427,6 +1427,92 @@ async def test_power_sensor_manager_creation(
     state = hass.states.get("sensor.battery_power_inverted")
     assert state is not None
     assert float(state.state) == -100.0
+    assert state.attributes[ATTR_UNIT_OF_MEASUREMENT] == UnitOfPower.WATT
+
+
+async def test_power_sensor_inverted_propagates_unit(
+    recorder_mock: Recorder, hass: HomeAssistant
+) -> None:
+    """Test inverted power sensor copies unit from the source state."""
+    assert await async_setup_component(hass, "energy", {"energy": {}})
+    manager = await async_get_manager(hass)
+    manager.data = manager.default_preferences()
+
+    # Use a non-default unit to prove we copy from the source rather than
+    # hard-coding Watts.
+    hass.states.async_set(
+        "sensor.battery_power",
+        "1.5",
+        {ATTR_UNIT_OF_MEASUREMENT: UnitOfPower.KILO_WATT},
+    )
+    await hass.async_block_till_done()
+
+    await manager.async_update(
+        {
+            "energy_sources": [
+                {
+                    "type": "battery",
+                    "stat_energy_from": "sensor.battery_energy_from",
+                    "stat_energy_to": "sensor.battery_energy_to",
+                    "power_config": {
+                        "stat_rate_inverted": "sensor.battery_power",
+                    },
+                }
+            ],
+        }
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.battery_power_inverted")
+    assert state is not None
+    assert float(state.state) == -1.5
+    assert state.attributes[ATTR_UNIT_OF_MEASUREMENT] == UnitOfPower.KILO_WATT
+
+    # Source switches to Watts — the inverted sensor should follow.
+    hass.states.async_set(
+        "sensor.battery_power",
+        "200.0",
+        {ATTR_UNIT_OF_MEASUREMENT: UnitOfPower.WATT},
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.battery_power_inverted")
+    assert state is not None
+    assert float(state.state) == -200.0
+    assert state.attributes[ATTR_UNIT_OF_MEASUREMENT] == UnitOfPower.WATT
+
+
+async def test_power_sensor_inverted_source_without_unit(
+    recorder_mock: Recorder, hass: HomeAssistant
+) -> None:
+    """Test inverted sensor reports no unit when source has none."""
+    assert await async_setup_component(hass, "energy", {"energy": {}})
+    manager = await async_get_manager(hass)
+    manager.data = manager.default_preferences()
+
+    hass.states.async_set("sensor.battery_power", "100.0")
+    await hass.async_block_till_done()
+
+    await manager.async_update(
+        {
+            "energy_sources": [
+                {
+                    "type": "battery",
+                    "stat_energy_from": "sensor.battery_energy_from",
+                    "stat_energy_to": "sensor.battery_energy_to",
+                    "power_config": {
+                        "stat_rate_inverted": "sensor.battery_power",
+                    },
+                }
+            ],
+        }
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.battery_power_inverted")
+    assert state is not None
+    assert float(state.state) == -100.0
+    assert ATTR_UNIT_OF_MEASUREMENT not in state.attributes
 
 
 async def test_power_sensor_manager_cleanup(