diff --git a/src/nwp500/converters.py b/src/nwp500/converters.py
index d2a88e8..8e53b16 100644
--- a/src/nwp500/converters.py
+++ b/src/nwp500/converters.py
@@ -27,6 +27,7 @@
     "device_bool_from_python",
     "tou_override_to_python",
     "div_10",
+    "mul_10",
     "enum_validator",
     "str_enum_validator",
     "half_celsius_to_preferred",
@@ -123,6 +124,29 @@ def div_10(value: Any) -> float:
     return float(value)
 
 
+def mul_10(value: Any) -> float:
+    """Multiply numeric value by 10.0.
+
+    Used for energy capacity fields where the device reports in 10Wh units,
+    but we want to store standard Wh.
+
+    Args:
+        value: Numeric value to multiply.
+
+    Returns:
+        Value multiplied by 10.0.
+
+    Example:
+        >>> mul_10(150)
+        1500.0
+        >>> mul_10(25.5)
+        255.0
+    """
+    if isinstance(value, (int, float)):
+        return float(value) * 10.0
+    return float(value)
+
+
 def enum_validator(enum_class: type[Any]) -> Callable[[Any], Any]:
     """Create a validator for converting int/value to Enum.
 
diff --git a/src/nwp500/enums.py b/src/nwp500/enums.py
index b9c4429..ae72667 100644
--- a/src/nwp500/enums.py
+++ b/src/nwp500/enums.py
@@ -7,7 +7,7 @@
 See docs/protocol/quick_reference.rst for comprehensive protocol details.
 """
 
-from enum import Enum, IntEnum
+from enum import IntEnum, StrEnum
 
 # ============================================================================
 # Status Value Enumerations
@@ -239,7 +239,7 @@ class VolumeCode(IntEnum):
     VOLUME_80 = 3  # NWP500-80: 80-gallon (302.8 liters) tank capacity
 
 
-class InstallType(str, Enum):
+class InstallType(StrEnum):
     """Installation type classification.
 
     Indicates whether the device is installed for residential or commercial use.
diff --git a/src/nwp500/models.py b/src/nwp500/models.py
index 2c480d8..804e91f 100644
--- a/src/nwp500/models.py
+++ b/src/nwp500/models.py
@@ -29,6 +29,7 @@
     enum_validator,
     flow_rate_to_preferred,
     half_celsius_to_preferred,
+    mul_10,
     raw_celsius_to_preferred,
     tou_override_to_python,
     volume_to_preferred,
@@ -68,6 +69,7 @@
 DeviceBool = Annotated[bool, BeforeValidator(device_bool_to_python)]
 CapabilityFlag = Annotated[bool, BeforeValidator(device_bool_to_python)]
 Div10 = Annotated[float, BeforeValidator(div_10)]
+TenWhToWh = Annotated[float, BeforeValidator(mul_10)]
 HalfCelsiusToPreferred = Annotated[
     float, WrapValidator(half_celsius_to_preferred)
 ]
@@ -416,14 +418,14 @@ class DeviceStatus(NavienBaseModel):
             "False = device follows TOU schedule normally"
         )
     )
-    total_energy_capacity: float = Field(
+    total_energy_capacity: TenWhToWh = Field(
         description="Total energy capacity of the tank in Watt-hours",
         json_schema_extra={
             "unit_of_measurement": "Wh",
             "device_class": "energy",
         },
     )
-    available_energy_capacity: float = Field(
+    available_energy_capacity: TenWhToWh = Field(
         description=(
             "Available energy capacity - "
             "remaining hot water energy available in Watt-hours"
diff --git a/tests/test_model_converters.py b/tests/test_model_converters.py
index 4eb5f5b..cfb940e 100644
--- a/tests/test_model_converters.py
+++ b/tests/test_model_converters.py
@@ -15,6 +15,7 @@
     device_bool_to_python,
     div_10,
     enum_validator,
+    mul_10,
     tou_override_to_python,
 )
 from nwp500.enums import DhwOperationSetting, OnOffFlag
@@ -242,6 +243,78 @@ def test_known_values(self, input_value, expected):
         assert result == pytest.approx(expected, abs=0.001)
 
 
+class TestMul10Converter:
+    """Test mul_10 converter (multiply by 10).
+
+    Used for energy capacity fields where the device reports in 10Wh units,
+    but we want to store standard Wh.
+    Only multiplies numeric types (int, float), returns float(value) for others.
+    """
+
+    def test_zero(self):
+        """0 * 10 = 0.0."""
+        assert mul_10(0) == 0.0
+
+    def test_positive_value(self):
+        """100 * 10 = 1000.0."""
+        assert mul_10(100) == 1000.0
+
+    def test_negative_value(self):
+        """-50 * 10 = -500.0."""
+        assert mul_10(-50) == -500.0
+
+    def test_single_digit(self):
+        """5 * 10 = 50.0."""
+        assert mul_10(5) == 50.0
+
+    def test_float_input(self):
+        """50.5 * 10 = 505.0."""
+        assert mul_10(50.5) == 505.0
+
+    def test_string_numeric(self):
+        """String '100' is converted to float without multiplication."""
+        # mul_10 converts non-numeric to float but doesn't multiply
+        result = mul_10("100")
+        assert result == pytest.approx(100.0)
+
+    def test_energy_capacity_example(self):
+        """Test with realistic energy capacity values from issue #70."""
+        # Device reports 1404.0 (10Wh units), should convert to 14040.0 Wh
+        device_value = 1404.0
+        expected_wh = 14040.0
+        assert mul_10(device_value) == expected_wh
+
+    def test_large_value(self):
+        """1000 * 10 = 10000.0."""
+        assert mul_10(1000) == 10000.0
+
+    def test_very_small_value(self):
+        """0.1 * 10 = 1.0."""
+        assert mul_10(0.1) == 1.0
+
+    def test_negative_small_value(self):
+        """-0.5 * 10 = -5.0."""
+        assert mul_10(-0.5) == -5.0
+
+    @pytest.mark.parametrize(
+        "input_value,expected",
+        [
+            (0, 0.0),
+            (10, 100.0),
+            (50, 500.0),
+            (100, 1000.0),
+            (1000, 10000.0),
+            (-100, -1000.0),
+            (1.5, 15.0),
+            (99.9, 999.0),
+        ],
+    )
+    def test_known_values(self, input_value, expected):
+        """Test known mul_10 conversions for numeric types."""
+        result = mul_10(input_value)
+        assert result == pytest.approx(expected, abs=0.001)
+
+
 class TestEnumValidator:
     """Test enum_validator factory function.