I'm going to opt for it to be a turbolift since there are no other episodes (AFAIK) to suggest differently. Keeping it simple
The "Turbolift 2" label appears there in a few different episodes in Season 3 but Battlefield
is the only one where the doors open (they do it again towards the end of the ep as well, when Bele and Lokai begin their chase)
I originally thought about using the markings on the bottom of the engineering hull as guides for:
Circle - the M/AM reactor,
T-shape - AM fuel ejection,
Square - M/AM refueling ports,
Rectangle - extendable sensor antenna
and Red Rectangle - workbee hatch/pass-through to hangar
Some of these ideas stemmed from other blueprints and ideas I've read over the years. I had hoped that after piecing the interiors together, that they would line up with the exterior
Alas, only some align up and I discovered that the movie Enterprise also has similar markings. But upon further inspection it became apparent to me that they couldn't serve the same functions that I was thinking about and I chucked those ideas...
You mean these markings?
They were only added to the Enterprise-A (of which we saw precious little of the interior). Have a look at TMP and there's not a marking to be seen. Captain Robert April
began a project a while ago to incorporate these hatch markings into a functional layout for the E-A, but it seems to be on hiatus at the moment.
So, back to the red rectangle. Interestingly, it is right behind the hangar with no overlap and can be it's own compartment. I am now thinking it could be for a hatch to open and deploy emergency markers, towed sensor array, etc or an attachment point for a trailing boom with an ion pod at the end of it
I'm not 100%, but it seems that the red rectangle would cut accross two sections, here:
Am I close?