Replace CMOS system battery in Laptop

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I have a IBM Thinkpad T43 - 2668  Model 49U laptop.  The CMOS (system)
battery must be dead because I have to retype the date and time every
time I turn it on.  Unlike the desktop computers where you just pop in
a button battery, this laptop has the battery in a little case with 2
wires coming out and going to a plug.  I live in an area where there
are no real computer stores.  I tried to find it online and all I get
is Ebay.  I would not buy from Ebay if my life depended on it,
particularly electronics.  I emailed IBM a week ago or more and have
not gotten a reply.  I bet I've spent 5 or 6 hours trying to locate
this battery, and I'm done looking.  I know it's a 3 volt battery.  I
see no reason I cant just take a standard button battery and solder on
the wires from the old one, then wrap it in electrical tape.  My
question is this: How much heat can these batteries withstand to
solder on the wires?  My other option would be to see if Radio Shack
or some place like it has a "battery holder" for it, and solder the
wires to that.  Or maybe I can even remove one from an old
motherboard.  I must say this is a very stupid way to install the
battery.  I'm sure they could have put a socket in the computer for a
standard button battery.  I also wonder why the power battery dont
keep the CMOS set ????

Or does anyone know where to buy these things?



Re: Replace CMOS system battery in Laptop

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Please use paragraphs: it makes your messgae a lot easier to read
on screen and to snip to the relevant points.

Although I've done it before, I wouldn't recommend soldering directly
onto a regular button battery: for a start you need a reasonably
powerful iron and secondly there tends to be a corrosion-resistant
finish to them that is not the best thing to solder to.

However, batteries are readily available with solder tags already
fitted and those represent a much better way to go.  Most IBM
laptops I've seen use CR2032 cells.  A local (to me) supplier has
several tagged types listed, e.g.
but you shouldn't have much difficulty tracking something similar

Solder the wires from the old battery on and insulate, ideally with
a nice sized piece of heatshrink but anything will do.  Only gotcha
is that some models of IBM laptop have a relatively common failure
mode where they start eating CMOS batteries, and there's no way
around that short of a system board replacement.  I don't know if
the T43 is an affected model but it is possible your new battery
may only last for a couple of weeks if that is the case.

Andrew Smallshaw

Re: Replace CMOS system battery in Laptop wrote:
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Contacts like that, would be spot welded, rather than soldered.
Soldering would require raising the battery to a high temperature.

(Example of spot welded coin cell with tabs)

    "Another application is spot welding straps to nickel-cadmium or
     nickel-metal-hydride cells in order to make batteries. The cells
     are joined by spot welding thin nickel straps to the battery terminals.
     Spot welding can keep the battery from getting too hot, as might
     happen if conventional soldering were done."

If you could locate a PCB mount style battery socket, you could
solder wires to that, and then install a battery into the socket
after it has cooled. But such a scheme, would require plenty of
room inside the laptop, for the finished assembly.

( )

To make an insulating package, you can use heat shrink tubing.
Even without shrinking it, it still forms a protective cover.

The largest I see on Fry's, is 1.5" tubing. That might not be
big enough, but if you're ordering the socket anyway, toss in a
strip of that stuff, and see if it fits. I stock maybe four or
five sizes of shrink wrap here, for home projects.


One issue with buying a pre-built ("exact") replacement, is the
age of the battery supplied. If stock moves slowly, the battery
could already be years old. While shelf life of those batteries
is pretty good, you could still potentially get ripped off. I
remember buying watch batteries from a "battery store" in the mall,
and getting two flat batteries from them. So be careful where you buy
them from. Now, I only buy from places I know have significant
foot traffic (a large department store near me). That way, the
batteries you get might only be a year old.


Re: Replace CMOS system battery in Laptop

On Mon, 28 Mar 2011 21:44:17 -0600, wrote:

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Re: Replace CMOS system battery in Laptop

On 3/28/2011 11:44 PM, wrote:
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Look at this page:

The breakout board and coin cell holder you could use are both listed.
Damned expensive but it is an odd bit of kit that I've not seen elsewhere.

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