diff --git a/battery_inverters/sma_sunny_island/firmware.lua b/battery_inverters/sma_sunny_island/firmware.lua
index 921df1eb..7ad56a97 100644
--- a/battery_inverters/sma_sunny_island/firmware.lua
+++ b/battery_inverters/sma_sunny_island/firmware.lua
@@ -21,6 +21,12 @@ function send_properties()
   if sma then
     properties.serial_num = sma:read_u32_fix0(30057)
     properties.model = parse_model(sma:read_u32_enum(30053))
+
+    local nominal_capacity_ah = sma:read_u32_fix0(40031)
+    local nominal_voltage = sma:read_u32_fix0(40037)
+    if nominal_capacity_ah and nominal_voltage then
+      properties.nominal_capacity = nominal_capacity_ah * nominal_voltage / 1000
+    end
   end
 
   local values, err = config.read_all()
diff --git a/battery_inverters/sma_sunny_island/manifest.yml b/battery_inverters/sma_sunny_island/manifest.yml
index 6825519a..559e5853 100644
--- a/battery_inverters/sma_sunny_island/manifest.yml
+++ b/battery_inverters/sma_sunny_island/manifest.yml
@@ -31,6 +31,9 @@ properties:
   unit_id:
     display_name: Modbus Unit ID
     type: integer
+  nominal_capacity:
+    display_name: Nominal Capacity, kWh
+    type: float
 
 telemetry:
   status: