buickanddeere
Super Member
The more I think about it the more I'm in favour of the battery warmer with a maintainer along with the block heater.
The plug is sealed in with some sort of loctite, you could try heating the plug with a propane torch to melt the glue before attempting it again with a breaker bar.
That said, on mine I both heated the plug and used short quick taps from my impact gun to loosen it and backed it out with a socket extension from there.
Raised on a Deere - did you get the block heater installed? I just want to be sure everything worked out.