How do i filter the msg.payload output from a Tesla Node. So that I have only the output "battery_level" value that I can send with a Mqtt node to a Domoticz Device with IDX 1
On this particular question (getting values from a message) - there’s a great page in the docs that will explain how to use the debug panel to find the right path to any data item.
To answer your immediate question, i would use a change node to setmsg.payload to msg.payload.battery_level then connect the change node to an MQTT out node (with appropriate topic set).
As you are new to node-red - I highly recommend watching this playlist: Node-RED Essentials. It is by the developers of node-red. They're nice & short and to the point. You will understand a whole lot more in less than an hour. A small investment for a lot of gain.
And it really is as simple as I said: Attach a change node to your MQTT in, set msg.payload to msg.payload.battery_level link that to an MQTT out node
TBH, this is one of the most basic and fundamentals of node-red. You would do yourself a great favour watching that playlist (and perhaps work your way through the cookbook)