> I've never heard of a rechargeable PRAM battery.
> Could it be that the tech was talking only about the fuse for the main
> battery. To my knowledge there is no charging circuit for the PRAM
> battery.
> Please correct me if I'm wrong.
>
> Dean
>
>
The PRAM battery on many, if not all, (I have only checked on models
that I have owned) powerbooks is used to not only maintain the contents
of PRAM but also to maintain the contents of RAM while you swap out the
main battery during SLEEP. The Apple documents say that for instance, on
my PB 3400 and on my Duo-280c that the PRAM battery should give you up
to 4 minutes to swap main batteries while the computer is in SLEEP mode.
If you take longer, the PRAM battery will become completely depleted and
you lose it all. Also, if your PRAM battery is not fully charged up OR
if it is dying of old age (can't hold a full capacity charge) then you
might not get 4 minutes to change out a main battery while in sleep
mode. In fact, your PRAM battery may work well enough to maintain your
time and date and other PRAM settings, but it may be poor enough
(effective "high internal resistance" caused by old age) that it can't
supply the larger amount of current required to maintain RAM contents
while swapping out the main battery during sleep.
Since the PRAM battery is supplying a relatively large amount of power
during a SLEEPing main battery swap, it becomes partially discharged.
And, since it is a desirable trait to be able to swap out the main
battery while sleeping, the PRAM battery has to be made of "secondary"
(rechargeable) cell(s) rather than "primary" (non-rechargeable) cell(s).
A desktop computer doesn't require a capability of "maintaining RAM"
while a battery is swapped in sleep mode, therefore the desktop computer
can, and does use a non-rechargeable PRAM battery.
The PRAM itself uses very little power, but RAM uses considerably more power.
Greg
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