Hot swapping CMOS batteries

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The standard instructions for changing out a desktop CMOS battery say you  
should turn everything off and unplug the power cord.  But I wonder if guys  
who do this kind of stuff for a living don't hot swap the batteries with the  
power on, or at least leave the power cord plugged in so the always-on 5V  
supply provide power to the CMOS.  That should prevent losing the contents of  
the CMOS memory, including the TOD and the BIOS settings.

On a related question, I also have an old Toshiba Satellite L35 laptop that  
I'd like to replace the CMOS battery on.  It looks like I would have to take  
the entire laptop apart so I can remove the motherboard, turn it over, and  
replace the battery.  Or, it turns out I can see the battery through the side  
of the wireless compartment, and I should be able the cut a window in the  
bottom of the case through which I could switch out the battery, then hot-
glue the window back in place.  Is there any reason not to do it that way?  
It's a lot more likely the laptop would survive the latter procedure.



Re: Hot swapping CMOS batteries
On 11/01/2017 05:42, Peabody wrote:
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Yes,  I added a tag to the battery line, so I could easily swap the  
battery , while jumpering in an external battery supply with a bit of a  
dropper resistor

Re: Hot swapping CMOS batteries
On 1/10/2017 9:42 PM, Peabody wrote:
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Problem with doing anything with the power on is the unexpected.
Suggest you at least put some tape on the battery so you have
something to hold onto while you try to pry it out.

The other issue is the reset.  Assuming you have a reason/symptom
to change the battery, it may be that the state of the memory is
compromised.  I've had laptops with rechargeable CMOS batteries
that wouldn't run after I manually recharged them.
Removing/waiting/replacing the charged battery fixed it.

Re: Hot swapping CMOS batteries

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There doesn't seem to be any logic to hot swapping a CMOS battery - many  
motherboards have a jumper header to discharge the smoothing caps on the RTC  
rail - it holds for at least a few minutes with the battery out.

Usually you don't even know it needs replacing till boot up reports a CMOS  
checksum error - then I just fit a new battery and load optimum defaults.  
There's only a couple of values I need to set manually.  


Re: Hot swapping CMOS batteries
On 11/01/2017 20:14, Benderthe.evilrobot wrote:
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The clue for me , is progressively worsening internal clock timekeeping.
Incidently , hot soldering a tag, remove the power from the soldering  
iron before soldering , while still hot

Re: Hot swapping CMOS batteries
On 2017/01/11 12:56 PM, N_Cook wrote:
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Propane soldering irons work very well for this sort of thing -  
ungrounded...

John :-#)#

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Re: Hot swapping CMOS batteries
On Wed, 11 Jan 2017, John Robertson wrote:

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Wasn't that one reason for promoting the cordless soldering iron sold in  
the seventies?  I forget who made it, Radio Shack sold it under their  
name also, but there was something about an "iso-tip". Since it didn't  
plug in, you could use it where other irons might not be safe.

   Michael


Re: Hot swapping CMOS batteries
snipped-for-privacy@ncf.ca says...
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Wal made them, maybe still do. They started out making battery powered  
shavers.  Maybe that was just another product to that line.  The main  
usage was for places that you did not or could not get a cord to.  I had  
one and used it because it was quick heating when I only wanted to make  
one or two quick connections. Did not have to wait for the wall powered  
unit to heat up.  Now I have an iron that heats up in just a few  
seconds.




Re: Hot swapping CMOS batteries
Michael Black wrote:

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  > didn't plug in, you could use it where other irons might not be safe.


    Wahl made, and still makes them.


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Never piss off an Engineer!

They don't get mad.

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Re: Hot swapping CMOS batteries
On Sat, 14 Jan 2017, Michael A. Terrell wrote:

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Thanks.  I suddenly couldn't remember who made it.

   Michael


Re: Hot swapping CMOS batteries
Michael Black wrote:
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    You're welcome. :)


--  
Never piss off an Engineer!

They don't get mad.

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Re: Hot swapping CMOS batteries

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Even so - I wouldn't bother hot swapping a soldered in CMOS battery.  


Re: Hot swapping CMOS batteries

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IME: The time and date data usually survives - but it surprises me every  
once in a while.  


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