Measuring CMOS Battery charge

[Dave]

Maybe a silly question but I'd like to know as it's way outside my
knowledge base... :-)

On my old (28.5 years) SARPC, a long time ago I moved the CMOS battery
from the Mobo up into the gutter top side of the second slice.

I was wondering, did anyone ever write an app that would measure and
display the state of the CMOS battery, or even if that is possible?

Thanks
Dave

[Theo]

Post by Dave
Maybe a silly question but I'd like to know as it's way outside my
knowledge base... :-)
On my old (28.5 years) SARPC, a long time ago I moved the CMOS battery
from the Mobo up into the gutter top side of the second slice.
I was wondering, did anyone ever write an app that would measure and
display the state of the CMOS battery, or even if that is possible?

There's no sensors on the CMOS battery, so there's no way of reading it. If
you can stick a multimeter on it you can measure the terminal voltage which
gives you some idea of its state (dead or not), but it won't give you much
accuracy about future lifetime.

Unlike a phone or laptop, there's no 'gas gauge' monitoring hardware to
measure how much energy has gone out of it, and to add such monitoring to
such a small battery would end up draining the battery much faster so
there's no point.

You could put a digital voltmeter circuit on it so you could read the
voltage from software, but would need to design it so that it doesn't cause
additional drain.

Theo

[Dave]

Post by Theo

Post by Dave
Maybe a silly question but I'd like to know as it's way outside my
knowledge base... :-)
On my old (28.5 years) SARPC, a long time ago I moved the CMOS battery
from the Mobo up into the gutter top side of the second slice.
I was wondering, did anyone ever write an app that would measure and
display the state of the CMOS battery, or even if that is possible?

There's no sensors on the CMOS battery, so there's no way of reading it.
If you can stick a multimeter on it you can measure the terminal
voltage which gives you some idea of its state (dead or not), but it
won't give you much accuracy about future lifetime.
Unlike a phone or laptop, there's no 'gas gauge' monitoring hardware to
measure how much energy has gone out of it, and to add such monitoring
to such a small battery would end up draining the battery much faster so
there's no point.
You could put a digital voltmeter circuit on it so you could read the
voltage from software, but would need to design it so that it doesn't
cause additional drain.
Theo

Thanks for the info, appreciated.

I don't use the old SARPC very often these days, but I run it for a while
at least once week regardless...
So once a month while the SARPC is ON, I take the lid off and check the
rechargeable battery voltage is still okay.

That's all I really need to know. :-)

Dave

[David Higton]

Post by Dave

Post by Theo

Post by Dave
Maybe a silly question but I'd like to know as it's way outside my
knowledge base... :-)
On my old (28.5 years) SARPC, a long time ago I moved the CMOS battery
from the Mobo up into the gutter top side of the second slice.
I was wondering, did anyone ever write an app that would measure and
display the state of the CMOS battery, or even if that is possible?

There's no sensors on the CMOS battery, so there's no way of reading it.
If you can stick a multimeter on it you can measure the terminal voltage
which gives you some idea of its state (dead or not), but it won't give
you much accuracy about future lifetime.
Unlike a phone or laptop, there's no 'gas gauge' monitoring hardware to
measure how much energy has gone out of it, and to add such monitoring to
such a small battery would end up draining the battery much faster so
there's no point.
You could put a digital voltmeter circuit on it so you could read the
voltage from software, but would need to design it so that it doesn't
cause additional drain.
Theo

Thanks for the info, appreciated.
I don't use the old SARPC very often these days, but I run it for a while
at least once week regardless... So once a month while the SARPC is ON, I
take the lid off and check the rechargeable battery voltage is still okay.
That's all I really need to know. :-)

The only problem that you /might/ have is that once a month may or may
not be enough to make up for the discharge during the rest of the time.
It's not easy to calculate whether x minutes of use every y days is or
is not enough - and in any case you probably don't use it on a fully
predictable cycle.

In the end, all it means is that, if one day it doesn't boot up with
the correct settings, keep it powered on for a good few hours to charge
the battery up again.

Also, you may find it more useful to check the battery's voltage before
you switch on, rather than after, while it's charging.

David

[Dave]

[Snip]

Post by David Higton

Post by Dave
Thanks for the info, appreciated.
I don't use the old SARPC very often these days, but I run it for a
while at least once week regardless... So once a month while the SARPC
is ON, I take the lid off and check the rechargeable battery voltage
is still okay.
That's all I really need to know. :-)

The only problem that you /might/ have is that once a month may or may
not be enough to make up for the discharge during the rest of the time.
It's not easy to calculate whether x minutes of use every y days is or
is not enough - and in any case you probably don't use it on a fully
predictable cycle.
In the end, all it means is that, if one day it doesn't boot up with
the correct settings, keep it powered on for a good few hours to charge
the battery up again.
Also, you may find it more useful to check the battery's voltage before
you switch on, rather than after, while it's charging.
David

Generally good advice...

In my case, the running once a week is usually for at least four hours.

I usually test the voltage before starting the computer to get a truer
battery reading.
But then occasionally once the computer *is running* I take the battery
out of its holder and test it, and if it's showing signs of being a bit
low, I temporarily put another battery in the holder, then take the
rechargeable elsewhere to put it on charge for much longer.

Then when charged up, putting it back inside the (Obviously running)
computer.

I've been doing this for many years (15) and not *yet* lost any CMOS
settings.

Which is more than can be said about the number of times the VRPC CMOS has
gone crapola. :-)

No biggy of course, as any long time user of Virtual Acorns knows, keep
regular backups of the CMOS file. :-)

Dave

[David Higton]

Post by Dave
In my case, the running once a week is usually for at least four hours.
I usually test the voltage before starting the computer to get a truer
battery reading. But then occasionally once the computer *is running* I
take the battery out of its holder and test it, and if it's showing signs
of being a bit low, I temporarily put another battery in the holder, then
take the rechargeable elsewhere to put it on charge for much longer.
Then when charged up, putting it back inside the (Obviously running)
computer.
I've been doing this for many years (15) and not *yet* lost any CMOS
settings.
Which is more than can be said about the number of times the VRPC CMOS has
gone crapola. :-)
No biggy of course, as any long time user of Virtual Acorns knows, keep
regular backups of the CMOS file. :-)

Clearly you have a good system in place!

David