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From: b11_ on 15 Dec 2009 19:51
Seeking utility that checks the motherboard battery.
From: Shenan Stanley on 15 Dec 2009 20:28
b11_ wrote:
> Seeking utility that checks the motherboard battery.

Most efficient/sure way...

Remove the battery, spend the $1, replace the battery.

--
Shenan Stanley
MS-MVP
--
How To Ask Questions The Smart Way
http://www.catb.org/~esr/faqs/smart-questions.html


From: Rey Santos on 16 Dec 2009 03:28
Voltages are shown on the BIOS setup under something like PCHealth if your
motherboard supports it. However, the CMOS (VBAT) battery may indicate the
correct voltage because it has already recharged. A dying battery can still
recharge but loses charge quickly after shutdown. Indications of dying/dead
battery CMOS bad checksum error on first boot where you need to press F1 to
continue and the date and time gets reset.

--
Rey


"b11_" wrote:

> Seeking utility that checks the motherboard battery.
From: Paul on 16 Dec 2009 07:18
Rey Santos wrote:
> Voltages are shown on the BIOS setup under something like PCHealth if your
> motherboard supports it. However, the CMOS (VBAT) battery may indicate the
> correct voltage because it has already recharged. A dying battery can still
> recharge but loses charge quickly after shutdown. Indications of dying/dead
> battery CMOS bad checksum error on first boot where you need to press F1 to
> continue and the date and time gets reset.
>

The CR2032 and associated circuitry in the computer, is specifically
designed *not* to charge the battery. The battery manufacturer doesn't
want anyone pumping current into it. Accidental charging current (an
unavoidable aspect of the way the circuit is designed) is limited to
1 microamp. And this value is established by the leakage characteristics
of the typical diodes used to prevent battery charging.

http://data.energizer.com/PDFs/cr2032.pdf

Max Rev Charge: 1 microampere <--- charging by accident, not on purpose

That means if there was charging current, it is basically limited
to the max leakage in a typical diode being used to enforce
forward conduction only.

If you scroll to the very bottom of this document, Figure 6 has
an equivalent circuit for motherboard applications.

http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_Lithium_PrevQualityProblems.pdf

The battery circuit has a series resistor (the "squiggle" above the
battery). The thing after that, is the diode (inverted triangle with
bar on top). The diode enforces unidirectional current flow, in this
case, out of the battery. If the diode is reverse biased (by the circuit
attempting to charge the battery), the diode stops the current flow.
Since the diode is not perfect, at high temperatures, like 100C,
the diode may leak up to 1 microamp of current. The energizer datasheet
is adjusted to match that reality, so that a designer can use a
Schottky diode. Schottky diodes are preferred for their low
Vfb forward bias voltage drop. I'm sure Energizer doesn't want any
current in there, but allowing a value of 1 microampere makes it possible
for the circuit shown in the Panasonic document to be used.

A worst case scenario for battery usage would be

1) Use the computer for eight hours a day (typical work day).
2) Unplug the computer at the end of the day. Time keeping runs from
the CR2032. You're saving on your AC power bill. But this shortens
the battery life.

Such a usage scenario results in a three year battery life.

A second usage scenario would be

1) Computer user uses the computer normally. Hours of usage
don't matter.
2) At the end of a session, the user places the computer in standby via
"Turn Off Computer" : "Standby". That is standby suspend to RAM (S3).
The computer power supply provides juice for time keeping, from +5VSB.
No current flows out of the battery.

That usage scenario results in a ten year battery life (i.e. the same
as the shelf life of the battery roughly). Time keeping in that case,
is always supported by current flowing from the ATX power supply. The
computer must remain plugged in and switched on at the back. But the
fans don't have to be spinning. +5VSB runs as long as the switch
on the back is in the ON position.

*******

Not all computers have the ability to monitor VBAT in hardware.
And I've seen cases where the hardware monitor has a signal intended
for that purpose, but no utility seems to display any info about it.
I would not rely on a software utility to check the voltage, because
of the variety of hardware implementations. Using a multimeter to
check the battery (you can even leave the battery in place while
checking it), is a reliable way to check it. But this is not
something that people are going to be doing every day - as you
state, surveillance should start, if there is trouble noted with
time keeping when the computer sleeps, or if BIOS settings
are being lost (like which disk to boot from). That is the time
to dig out the multimeter.

*******

There was a time in the past, where at least some devices, used a
NiCD battery (rechargeable) to power standby circuitry. Such circuits are
notoriously bad, as the batteries used to leak and corrode
electrical connections and other hardware. The move to the
current Lithium battery scheme, prevents such damage.

Personally, I wait until the computer exhibits tell tale symptoms,
before bothering to check the CR2032 with a multimeter. It is too
much effort to be doing such a check regularly.

Paul
From: Jose on 16 Dec 2009 07:24
On Dec 15, 7:51 pm, b11_ <b...(a)discussions.microsoft.com> wrote:
> Seeking utility that checks the motherboard battery.

If you suspect it, replace it and be done with it.

Here come the volt meters and schematics...
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