I just sent my letter. In typing the letter, citing the various rules, I'm becoming of the opinion that it needs to be there.
It does not really fit the "loose item" bit. It is not, from what I've read here, prone to flopping about (the battery, otoh....hah). From what I've seen, though, reading here and looking at cars, it seems fairly well secured.
So, 18.104.22.168.B does not really cover it - not really a "loose item."
Then, the spare tire rule - nutshell, spare tires, jacks, associated stuff can come out, AS WELL AS things that rely on the jack/spare - so, if taking the jack/spare out CREATES a loose item, that's fair game, too.
Does not really apply in our case.
SO, unofficial interpretation (I'm not on the SEB, but was at one time), it should be there.
We should get a good answer, though - a current SEB member used to autocross an Elise in SS (Brian Conners).