600au: SRM setting doesn't stick?

I recently dragged out an alpha from storage.  According to the case,
it's a 600au.

It came up in what I think is ARC - a bunch of X3.64 escape sequences,
prompting for keystrokes like F2.  I found enough saved doc to use its
menu system minimally, and got it set to SRM.  And, with a bit of work,
I even got it to boot.  (The NetBSD/alpha I had on hand turned out to
be rather old - 2003 vintage 1.4T.  Cool that NetBSD that old runs on a
real 64bit machine!)

The reason I'm writing now is that the SRM setting doesn't seem to
stick.  If I turn it off for more than about 250ms, it reverts back to
ARC.  (To be precise, my sample size is two: the two times I have
turned it off after setting SRM and left it off for more than about
200-300 ms, it has reverted; I have used a fast power-cycle as a reset,
since the reset button doesn't seem to work in many cases, and it's
worked fine, but it has been a *fast* power-cycle, and the SRM setting
has survived those.)

Am I correct in thinking this just means it needs a battery
replacement, a la CMOS battery on i386 or amd64?  If so, can anyone
give me a pointer to where the battery hides?  It's a nicely made
chassis, mechanically, but it doesn't look particularly easy to
disassemble; I'd rather avoid taking it apart to the extent feasible.
So knowing where to look for the battery would be useful.  (I did take
a look inside it.  I didn't see anything that looked promising, but
only about half the main PCB was visible.)

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