Thanks John!
I did read all I could find on the forum and documentation-but it seems obsolete 
I did finally managed to get around it and have it reported as battery, but it’s useless as I can’t create scenes (which was one of my intentions), I can however create node red flows.
If you do want to go my route, you would need to bring up such values (which is quite easy via mqtt) and use them in scenes, I could only make them work if they are reported as temperature or humidity - I also tried as brightness (since sonoff devices have dimmer, but this doesn’t work, perhaps there are others)
One strange thing (why I said documentation might be obsolete), when I tried to use “temperature”, no matter what I selected as registered-device, it would always give me “invalid parameters” when I was trying to put-device-state. Worked with “humidity”
