MicroVAX 3500 questions

I have finally got my hands on a vax. The machine is a MicroVAX 3500
configured with 32MB RAM. As this is the first vax I have ever seen in
real life I now have a bunch of questions:

Behind the CPU panel there is a white battery attached to the PCB
(with the screen, switches, console port). What is this battery for
and how important is it? Does it need replacing or will the system be
fine without it? (It is making a bit of a mess at the moment)

Behind a grill in the top left corner of the case there is a panel of
four 8-pin ports. There are no cables going to these ports and there
is nothing plugged in to them. They are numbered 0-3. What are they
for?

I have read that the C-D slots in the BA213 QBus backplane are just a
C-D interconnect. What are the likely reasons for this sytem to have a
grant continuity card in slot 9CD and a "WQDHV/02" card installed in
slot 8CD? The system is missing the covers for slots 12, 11 and 10 -
maybe there used to be something installed in there?

The back of the case has two stickers. The second slightly covers the
first sticker. It contains a second model number "CA-MX47G-BD" and the
text "DUAL MV3500 PART#2" - what does this mean?

Im sure there are probably manuals out there that cover this sort of
thing but so far my searches have only turned up the manual for the
DELQA ethernet controller.

Any answers are much appreciated.
- David Goodwin
.