Replacing CMOS battery on motherboard
 

On Nov 8, 10:17 am, Paul wrote:
[...] CR2032's have to last all on their own,
no charging allowed. The max charge current allowed is 1 microamp,
so they're serious about allowing current to flow into them.
Current may only flow out.

A 3+ Megohm resistor would work then.

That tiny of a trickle charge might make a BIG difference.

I've seen SEVERAL mothballed systems with CR2032
batteries where resetting the clock, shutting them down
and then checking them later indicated their RTC was
running slow when the system was off.
Leaving them on for 4 hours or so SEEMED to
charge the CR2032 because the RTC began to
keep time accurately when systems were off.

Is it possible they actually implemented the
1 microamp trickle charge you implied?

I've actually seen this trick work several times.

I've also seen systems where the BIOS settings
were "forgotten" due to low battery and running
it for a day caused the battery to hold the settings.

Even if they used a 6 Megohm resistor to
charge the CR2032 battery at half a microamp I would
expect that would be enough to make a big
difference to that tiny battery.

Is there a reason that flash hasn't
replaced CMOS for BIOS settings?

Replacing CMOS battery on motherboard
 

In message
,
Greegor writes:
On Nov 8, 10:17 am, Paul wrote:
[...] CR2032's have to last all on their own,
no charging allowed. The max charge current allowed is 1 microamp,
so they're serious about allowing current to flow into them.
Current may only flow out.

A 3+ Megohm resistor would work then.

That tiny of a trickle charge might make a BIG difference.

I've seen SEVERAL mothballed systems with CR2032
batteries where resetting the clock, shutting them down
and then checking them later indicated their RTC was
running slow when the system was off.
Leaving them on for 4 hours or so SEEMED to
charge the CR2032 because the RTC began to
keep time accurately when systems were off.

Is it possible they actually implemented the
1 microamp trickle charge you implied?

I've actually seen this trick work several times.

I've also seen systems where the BIOS settings
were "forgotten" due to low battery and running
it for a day caused the battery to hold the settings.

That - and the clock running better - _could_ be explained just by a
capacitor having charged.

Even if they used a 6 Megohm resistor to
charge the CR2032 battery at half a microamp I would
expect that would be enough to make a big
difference to that tiny battery.

(It's not that tiny, either in size or capacity!) I suspect that the -
however minuscule - risk of leakage (or even explosion; there were some
cases with early lithium cells, though none I know of with a CR2032) is
sufficient to put off mobo manufacturers. People have long memories:
that batch of dud capacitors, for example, is still spoken of.

Is there a reason that flash hasn't
replaced CMOS for BIOS settings?

I can think of three reasons: (a) in cost-conscious cases,
battery-plus-CMOS is probably still cheaper; (b) I think it _has_ in
some cases; (c) you have to have a cell for the clock/calendar anyway,
so [especially in (a) cases] you might as well keep to what's known and
works.

The time for which a system is expected to run also varies widely,
especially between manufacturers (who want a good "refresh" cycle!) and
users. The cell running down can be seen as another trigger for the
consideration of system replacement, at least by the makers.
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"I'd give my right arm to be ambidextrous"

I already am largely ambisinistral.