Separate devices for the same physical devices

[AJediIAm]

Both the P1 and Sessy battery have separate devices for the device and it's controller. This is very uncommon in Home Assistant and against the best practices. There are very few counter examples to this rule.
Devices are supposed to combine all internal (and connected in case of the P1 meter) components into logical devices based of the perception of the user.

Looking at the specific entities, it would make sense if the energy prices is moved to the P1 meter. Even though this might not match the API, it does match the expectations of the user.

[PimDoos]

The seperation does designate two different devices:

• Sessy WiFi Dongle (with serial number starting with D)
• Sessy Battery (with serial number starting with A)

The dongle is connected to Home Assistant, and then provides entities for both the dongle and the battery.

Both of these devices can be swapped out interchangably. The seperation should ensure that when the WiFi dongle is replaced, all sensors for the battery should remain the same. Same for the P1 meter dongle and the electricity meter. Currently, the unique ID situation does not fully support this scenario, but the goal is to migrate it to the new situation.

Why these devices do not assume the correct name in your example is not clear to me. When I tested this, the devices show with their respective names, corresponding to the names on their stickers.

[AJediIAm]

Many devices have a dongel like this and very few implement it as a separate device. It's against the home assistant practices to do so.
If you look at the system integration, the network card and ssd are not separate devices even though they are physically seperate and swappable.

There are other / better ways to preserve the history when replacing (part of) a device. It doesn't need to be a separate device in home assistant.

[PimDoos]

Where did you read it is against the practices to split these devices? The guidance on the developer portal specifies:

If you connect a sensor to another device to read some of its data, it should still be represented as two different devices. The reason for this is that the sensor could be moved to read the data of another device.
source

As I read this, the Sessy P1 dongle should be a seperate device from the energy meters it connects to. As for Sessy Battery and Sessy WiFi dongle devices, you could argue these are part of the same system. But given they both have their own serial number and contain their own ESP32 running seperate firmware, I consider this to be a logical seperation.

The Shelly integration seperates energy meters per channel into a seperate device. You could argue the Sessy 'renewable energy' sensors should be their own device for each phase as well, in line with the developer docs.

I think this is a matter of interpretation. If you can point me to some concrete examples where devs have considered this as unwanted, I am willing to reconsider my viewpoint.

[AJediIAm]

I'm aware the developer docs don't specify when not to split a device and mostly focus on when to split devices.
The quote from the develop docs refers to a device like a bluetooth proxy.

The energy meters are probebly the best example to support my proposition. all of the core integrations show the P1 meter and the utility meter as the same device. All ESP32, raspberry pi, home wizard and other flavors of P1 meters have a single P1 device, or separate devices for electricity, gas and water.
I have not seen an example where the p1 meter was split from communication device.
Appliences such as washing machines also have an esp32 or separate wifi module. Sometimes, the serial number of the wifi model and appliance is shown separatly, but always in 1 device. If it's 1 box, it's 1 device.

The separate shelly channels example only applies to shelly devices with more than one channel and controlling more than one distinctly different (downstream) object.
All other shellies are a single device for the Shelly and the downstream device they control.
Similarly, if the P1 meter or battery module would connect to more than 1 meter or battery, a multi device setup would be justified. In all other cases, a single device should be use for the P1 meter and a single device should be used for the battery.

To summarize: my main argument to support this as a best practise is the consistancy with which this principle is implmented by the other integration. Devices are only split if they are distinctly different from a user perspective.

In this end, your opinion is the only one that matters.
As the author, it's your call.
I think it's an interesting acedemic discussion, but it doesn't make a big difference in the end.