Battery filter won’t unscrew

Don't know what panel your trying to remove.
On mine; you just peel back the rear door weather strip and pop the filter retainers out. You should've been doing that every oil change.
That might just be a maintenance scheduled warning that you can clear through the maintenance reset procedure.

 

There is a trick to it. Use a Phillips of course, and engage the tool lightly into that plastic screw and turn lefty-loosy trying not to press and the screw should back out. It's a captive screw, so unscrew until obviously loose and extract the panel.

 

Just get some Panel and Trim tools and use a thin one to pry under the panel. That will either put enough pressure on the screw to unscrew it or pop the panel out. The screw itself is actually pretty useless as the panel just snaps in place.

 

Yeah, the screw comes out a bit then the whole fastener needs to be pried out like other plastic fasteners.
Get ready for some gross chit.

Mine was totally clogged with dust bunnies. I don't think it had ever been cleaned since new. I cleaned it at ~233k miles.
Never got the code.
It's very cleanable. Just pinch off the worst of it, tap it on the ground, then to the sink.

I think the filter is different if you have a Li-ion or Ni-Mh pack.