This is a monitoring Node Red flow that listens on UDP port 18542 IPv4 for the Batrium broadcasts
Copy the contents of the flow file and import from the clipboard into node red - it should create a new flow.
Tested with a Watchmon4
HW ver 4.2
FW ver 4.8
Sw ver 2.0.12
Credit for the bulk of the parsers to Daniel Römer from his grafpi project: http://diytechandrepairs.nu/raspberry-solar/ and https://github.com/Batrium/WatchMonUdpListener
Gaps filled and clarifications from the Batrium datasheet: Watchmon SW 1.0.30 UDP Outbound protocol
The machine running node red must be able to access port 18542 UDP IPv4