>> Sure.  But that's no reason to push it.  The 10-year lifetime is
>> running out on many of them, and every drain the battery doesn't
>> have is that much more life that it has before it needs attention.
> I guess it's a philosophical issue... I figure if it's *going* to run
> out (sooner vs. later) then I should just *plan* on replacing it --

Sure, plan for it.  But no need to make that time arrive any sooner
than it has to; even if you know the resource will be exhausted
eventually, there's no need to drain it faster than you have to.

Of course, if replacing is easy enough that you'd rather do that than
deal with the various minor nuisances stopping the clock involves, go
ahead.  (I just find the clock issues the more minor....)

> I am constantly moving machines around and often leave them
> unattended for long periods of time (powered off).  And, very few
> have heads on them so dragging out a keyboard/monitor just to
> preserve a dying (and REPLACEABLE!) resource seems too much effort
> for me...

Oh, heavens, I just use serial console for that stuff.

> I figure the top hat has room for a very *small* cell.  Probably on
> the order of 30mAH (volume).

The PDF file for the 08/18 says 48mAh, and further says that "The
device places a nominal RAM and TIMEKEEPER® load of less than 520nA on
the batter at room temperature.  At this rate, the capacity consumption
life is...about 10.5 years.  Capacity consumption life can be extended
by applying Vcc or turning off the clock oscillator prior to system
power down.".  Depending on how much of its life it's had Vcc applied
for, and what temperatures it's been at, the datasheet contains
formulas for working out its expected lifetime (page 18 in the 08/18
datasheet, for example).  The formulas given imply that battery drain
with the clock stopped is ignorably small - that shelf life runs out
first.  This seems like a plausible approximation in practice, to me.

The 02/12 file does not have anything similar, but it seems likely that
the basic principles will be the same.

> Even a battery made up of 3 AA nonrechargeable cells (i.e. "penlight
> cells" from your local hardware/grocery store) will last "an
> eternity".

I'd use 2 cells (3V nominal) and I'd probably use AAA, not AA, but I
certainly agree with your point, that for batteries like that the
current drain even with the clock on is ignorable - shelf life runs out
way first.  You could probably even use batteries that are "dead" from
the point of view of flashlights and handheld videogames and such,
here; they can usually provide voltage, but not much power.

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