HardwareBanter - View Single Post

**MrTsquare** · December 20th 14, 07:58 PM posted to alt.comp.hardware.pc-homebuilt

In article , says...

MrTsquare wrote:
After buying a couple of 2032 cmos batteries last year to replace the
one in my 5-year old build. I sprung for a new build including an ASUS
Z97Pro series motherboard. Put that together in August 2014. recently,
the new build began losing time, ie the time would continue to display
the time that the system was last turned off. After resetting it a few
times and playing with the choice of Internet Time servers displayed in
Win7, I finally replaced the alledgedly 4 month old CMOS battery. Life
is good and now time marches on. ONLY 4 MONTHS ON A CMOS BATTERY??

T2

The important thing, is to keep track of how long the new ones last.
Long term, you may decide the motherboard has a problem.

*******

The battery should last a little less than 3 years, if the PC is
kept unplugged all the time (24 hours a day). If you run the PC 16
hours a day, and unplug each day for 8 hours, then you'd expect
9 years (or getting closer to the 10 year shelf life). If the
PC has +5VSB (motherboard green LED lit all the time, whether
sleep/hibernate/run), then there is no excuse for less than
ten years from the battery. In other words, if you don't switch
off at the back or unplug each day, the +5VSB provides the clock
current and not the battery.

The Asus motherboard box has a "Serial number" on the outside
sticker. The first two characters of the serial number are
the manufacturer date. My last purchase was "E4..........",
which would be 2014 May or so. So I know my CMOS battery,
even if the PC is left unplugged, the battery should last
another two years minimum.

These numbers are only approximate. They assume the Southbridge
CMOS well draws maybe 10 microamps or so. The CMOS battery
is only used, if the +5VSB is not running (the +5VSB runs that
green LED on the Asus motherboard surface and is proof the
supervisory circuits have power).

If you place the "Clear CMOS" jumper in the wrong position,
that could drain the battery. But you would figure that out,
based on how that messed up the settings. If the motherboard
has an electrical fault in that section of the design,
and draws more than 10 microamps, that too could
flatten the battery. There have been some defective motherboards,
where they drained one battery after another, in short order.
And it's some sort of motherboard problem.

Interesting, Paul. Your figures on their lifetime do match my more
limited experience as I am used to them lasting 5 years on a desktop. I
don't believe I have the green led you refer to but then I have the
whole thing turned off probably 20 hours a day, but then that's just
like the like old ones that lasted 5 years. The original box for the MB
is long gone and I'm not going to open the case to check, but the MB
manual is dated April 2014. What occurs to me is that the ASUS stock of
CMOS batteries may be old. Maybe they got a good deal on them 4 or 5
years ago... ;)

T2