When configuring NUT driver parameters ("Extra Arguments" on the web UI) the input field separates parameters by commas. So if you enter "port=auto,vendorid=123" it splits that into 2 key/value pairs.
This makes it impossible to enter values containing commas, like "runtimecal=210,100,600,50"
I had to edit ups.conf manually and mark it as immutable to prevent OPNsense from messing with it:
# chflags schg /usr/local/etc/nut/ups.conf
It'd be great to have a plaintext input option or a way to escape commas on the web UI.