diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0520079..a2fe08b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,12 @@
 # Changelog
 
+## v1.0.4
+* Changed: Fixed errors for `MinVoltageCellId`, `MinCellVoltage`, `MaxVoltageCellId` and `MaxCellVoltage` calculations
+* Changed: Improved error handling and output
+
 ## v1.0.3
 * Added: Check if provided values are string, integer or float
-* Changed: Time-To-Go can now be configured in the config file. When charging the battery it's calculating the time to 100% SoC and when discharging it's calculating the time to the SoC configured in the config file.
+* Changed: Time-To-Go can now be configured in the config file. When charging the battery it's calculating the time to 100% SoC and when discharging it's calculating the time to the SoC configured in the config file
 
 ## v1.0.2
 * Added: Timeout in order to disconnect the battery, if no new MQTT message is received after x seconds (configurable in `config.ini`)
diff --git a/dbus-mqtt-battery/dbus-mqtt-battery.py b/dbus-mqtt-battery/dbus-mqtt-battery.py
index dc2ef5e..c02be77 100644
--- a/dbus-mqtt-battery/dbus-mqtt-battery.py
+++ b/dbus-mqtt-battery/dbus-mqtt-battery.py
@@ -391,16 +391,16 @@ def on_message(client, userdata, msg):
                             battery_dict['/TimeToGo']['value'] = 60 * 60 * 24 * 30
 
                     if 'Voltages' in jsonpayload and len(jsonpayload['Voltages']) > 0:
-                        if 'MinVoltageCellId' not in jsonpayload['System']:
+                        if 'System' not in jsonpayload or 'MinVoltageCellId' not in jsonpayload['System']:
                             battery_dict['/System/MinVoltageCellId']['value'] = min(jsonpayload['Voltages'], key=jsonpayload['Voltages'].get)
 
-                        if 'MinCellVoltage' not in jsonpayload['System']:
+                        if 'System' not in jsonpayload or 'MinCellVoltage' not in jsonpayload['System']:
                             battery_dict['/System/MinCellVoltage']['value'] = min(jsonpayload['Voltages'].values())
 
-                        if 'MaxVoltageCellId' not in jsonpayload['System']:
+                        if 'System' not in jsonpayload or 'MaxVoltageCellId' not in jsonpayload['System']:
                             battery_dict['/System/MaxVoltageCellId']['value'] = max(jsonpayload['Voltages'], key=jsonpayload['Voltages'].get)
 
-                        if 'MaxCellVoltage' not in jsonpayload['System']:
+                        if 'System' not in jsonpayload or 'MaxCellVoltage' not in jsonpayload['System']:
                             battery_dict['/System/MaxCellVoltage']['value'] = max(jsonpayload['Voltages'].values())
 
                         if 'Sum' not in jsonpayload['Voltages']:
@@ -460,7 +460,7 @@ def __init__(
         self._dbusservice.add_path('/ProductId', 0xFFFF)
         self._dbusservice.add_path('/ProductName', productname)
         self._dbusservice.add_path('/CustomName', customname)
-        self._dbusservice.add_path('/FirmwareVersion', '1.0.3')
+        self._dbusservice.add_path('/FirmwareVersion', '1.0.4')
         # self._dbusservice.add_path('/HardwareVersion', '')
         self._dbusservice.add_path('/Connected', 1)