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Hot swapping CMOS batteries

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.

Reply to
Peabody
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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

Reply to
N_Cook

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.

Reply to
mike

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.

Reply to
Benderthe.evilrobot

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

Reply to
N_Cook

Propane soldering irons work very well for this sort of thing - ungrounded...

John :-#)#

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Reply to
John Robertson

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

Reply to
Michael Black

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.

Reply to
Ralph Mowery

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

Reply to
Benderthe.evilrobot

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

Reply to
Benderthe.evilrobot

Wahl made, and still makes them.

--
Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)
Reply to
Michael A. Terrell

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

Michael

Reply to
Michael Black

You're welcome. :)

--
Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)
Reply to
Michael A. Terrell

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