[BUG] MQTT Entity ID* Sensor.unnamed_device_

[GerritPost]

Describe the bug
every sensor and button provided by MQTT does not have an entity ID in home assistant. so a default is set for e.g. unnamed_device_27

default_entity_id, causes this issue.

To Reproduce
Used https://mqtt-explorer.com/ software to debug

MQTT Explorer response from the battery emulator (notice the default_entity_id) :

{"name":"Battery Cell Voltage 2","default_entity_id":"be_battery_voltage_cell2","unique_id":"BEbe__battery_voltage_cell2","device_class":"voltage","state_class":"measurement","state_topic":"BE/spec_data","unit_of_measurement":"V","value_template":"{{ value_json.cell_voltages[1] }}","device":{"identifiers":["battery-emulator"],"manufacturer":"DalaTech","model":"BatteryEmulator","name":"Battery Emulator"},"availability":[{"topic":"BE/status"}],"payload_available":"online","payload_not_available":"offline","enabled_by_default":true}

Results in: unnamed_device_27

When I modify it with MQTT Explorer back to object_id

{"name":"Battery Cell Voltage 2","object_id":"be_battery_voltage_cell2","unique_id":"BEbe__battery_voltage_cell2","device_class":"voltage","state_class":"measurement","state_topic":"BE/spec_data","unit_of_measurement":"V","value_template":"{{ value_json.cell_voltages[1] }}","device":{"identifiers":["battery-emulator"],"manufacturer":"DalaTech","model":"BatteryEmulator","name":"Battery Emulator"},"availability":[{"topic":"BE/status"}],"payload_available":"online","payload_not_available":"offline","enabled_by_default":true}

The result is: Entity ID* battery_emulator_battery_cell_voltage_2

Notice! I did not used MQTT before the change object_id TO default_entity_id
Because HA never had these sensors before, and this a 'new' connection. I assume this causes issues for me, not for other users that are updated their software.
#2174

Expected behavior
A usable Entity ID

Screenshots
If applicable, add screenshots to help explain your problem.

using default_entity_id:

Using object_id:

An overview of sensors in HA

Version and settings (please complete the following information):

• Please attach screenshot of configuration for easier debugging
• Software version: 10.7.0
• Battery used: BMW i3
• Inverter communication protocol: BYD Battery-Box HVS
• Hardware used for Battery-Emulator: LilyGo T-CAN
• GPIO controlled contactors: yes
• MQTT: yes

Home Assistant OS Core 2026.5.0
Supervisor 2026.04.2
Operating System 17.3
Frontend 20260429.3

[GerritPost]

@roy13 Do you know more about this?, Downgrading to 10.5 can be an easy answer to 'verify' if it will be fixed. But I am afraid that reproducing / verifying the fix will be harder if all the Entity ID's are already known in HA. Then other users will encounter this bug.

my wild guess is that if I do the following steps, it could also work for me at 10.7

• Downgrade BE to 10.5
• Enable MQTT
• verify correct Entity ID's in HA for all the sensors of the BE
• Upgrade BE to 10.7
• Magically works?

But as I said, new users will encounter this bug then. That's why I did not try this yet!

[roy13]

Dam, does this mean you have to edit every sensors ID like this https://www.home-assistant.io/docs/configuration/customizing-devices/
That sounds time consuming, hopefully myself or someone will find the time to read the guides to see if there is another way they can be discovered.

[GerritPost]

@roy13
I'm reading the HA docs and my suggestion is that we should add unique_id and default_entity_id

https://www.home-assistant.io/integrations/sensor.mqtt/#default_entity_id

Adding every sensor manually is not even a consideration in my mind :P

[gegere]

There is an AI assistant you can install in your HA this will make all these changes to the default_entity_id super simple.

[roy13]

@GerritPost unfortunatly we already use both.

void set_battery_voltage_attributes(JsonDocument& doc, int i, int cellNumber, const String& state_topic,
                                    const String& default_entity_id_prefix, const String& battery_name_suffix) {
  doc["name"] = "Battery" + battery_name_suffix + " Cell Voltage " + String(cellNumber);
  doc["default_entity_id"] = default_entity_id_prefix + "battery_voltage_cell" + String(cellNumber);
  doc["unique_id"] = topic_name + default_entity_id_prefix + "_battery_voltage_cell" + String(cellNumber);
  doc["device_class"] = "voltage";
  doc["state_class"] = "measurement";
  doc["state_topic"] = state_topic;
  doc["unit_of_measurement"] = "V";
  doc["value_template"] = "{{ value_json.cell_voltages[" + String(i) + "] }}";

[GerritPost]

@GerritPost unfortunatly we already use both.

void set_battery_voltage_attributes(JsonDocument& doc, int i, int cellNumber, const String& state_topic,
                                    const String& default_entity_id_prefix, const String& battery_name_suffix) {
  doc["name"] = "Battery" + battery_name_suffix + " Cell Voltage " + String(cellNumber);
  doc["default_entity_id"] = default_entity_id_prefix + "battery_voltage_cell" + String(cellNumber);
  doc["unique_id"] = topic_name + default_entity_id_prefix + "_battery_voltage_cell" + String(cellNumber);
  doc["device_class"] = "voltage";
  doc["state_class"] = "measurement";
  doc["state_topic"] = state_topic;
  doc["unit_of_measurement"] = "V";
  doc["value_template"] = "{{ value_json.cell_voltages[" + String(i) + "] }}";

I see yes, I misread that as object_id I've probably found the solution,

default_entity_id should contain sensor e.g.: sensor.be_battery_voltage_cellTest1

Will try to fix it tomorrow, and test it