@thomas-braun I thought about it first, but switch does not show power when in ON state with no load connected, don't think load needs to be connected for voltage reading. Tried it with load connected, still does not read voltage. Just in case, I filed an issue at Zigbee github regarding not able to read voltage.
The load voltage state will also not be usable for connection detection. The reason is simple:
A plug which is connected may update this state once every x minutes, with x usually being within the range of 5 to 300. If you power of the plug, it lacks the power to update the value, hence the state will remain at the last state sent by the plug. This is true for any state published by the plug.
There are very few devices which publish their states in a short interval. Most only post changes to their values, and even then have a minimum time difference between posting different values.
The available state has the same issue. It is generated by the adapter attempting to obtain a response from the device using a "ping request". In theory, all line powered devices should respond to ping requests. Unfortunately, there are line powered devices which report as "end devices" and as such will not report to ping requests, i.e. their status cannot easily be verified.
@ap2017 yes, the zigbee connection strenght fluctuates also in my case. Since I have only two devices yet, I suppose this becomes more smooth if I have more devices running that create a tighter mesh network. In some weeks I will have some more devices running, let's see.
@normhenderson If the instance connects, the whole problem is usually that not the right registers are configured. I do not have the Victron CCGX but you should carefully read the register documentation of the Victron device and set the right one up in the adapter instance. Regarding your question 2: In my "holding register tab" I cannot find a separate SLAVE ID information. What exactly are you referring to? ad 3: If you configured the right registers, you will find values behind the data objects.
I have to admit that the modbus is tricky if you are not familiar in the details of the protocol.