[Beowulf] Mobo battery life in constantly on systems?

Bruce Allen ballen at gravity.phys.uwm.edu
Mon Jul 30 00:53:53 PDT 2007

Hi David,

A couple of years ago we had a lot of CMOS battery deaths on systems that 
were about 3 years old (and virtually always powered on).  These were 
Intel consumer-grade motherboards.

In the past year, a large number of Supermicro Opteron motherboards had 
their batteries dying within a few months of arrival.  This was probably a 
batch of bad batteries, or the batteries were overheated (cooked!) during 
transport or storage of the motherboards.

The speed of chemical reactions is an exponential function of temperature. 
So even a short period of overheating during transport or storage can 
cause the chemical reactions within the battery to run rapidly towards 
completion.  At home, we keep our spare batteries in the refrigerator to 
counter this.

At some point we simply did a wholesale replacement of the motherboard 
batteries with fresh new ones.

The good news is that you can buy boxes of 100 name-brand CMOS batteries 
at very low cost (less than $1 per battery).  When you get a box, test one 
battery by discharging it across a resistor over a period of a week and 
measuring the number of milliamp-hours that it delivers.  If not within 
specs, return the batteries to the vendor saying that they are substandard 
and probably have not been properly stored.


On Fri, 27 Jul 2007, David Mathog wrote:

> The question: what is the expected motherboard battery lifetime in
> systems that are continuously on?
> Background:
> The question arises because it was necesary to cycle the power today
> on a couple of nodes by unplugging them and then plugging them
> back in again.  When one came back up the BIOS settings were gone.
> That wasn't evident until a keyboard and monitor were plugged in.
> Losing BIOS settings when power is removed is pretty much the
> classic symptom of a dead motherboard battery.
> These nodes are now about 5 years old, and that is about the average
> battery lifetime in PCs that are turned off every night.  However these
> nodes have been on 99.99% of that time, so presumably the drain on the
> battery should have been nil.  Shelf life for motherboard batteries is
> typically about 10 years. There is no info on how old the batteries were
> that went into these systems, but presumably Tyan goes through a lot of
> batteries and these were probably fresh when installed.
> So bottom line, is this just a freak event or would you expect the
> other motherboard batteries to also die soon?
> Thanks,
> David Mathog
> mathog at caltech.edu
> Manager, Sequence Analysis Facility, Biology Division, Caltech
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