CMOS batteries, what excactly is the difference?

[Unknown_K]

What is the difference between a CMOS battery for a 380 series and newer 600 series and the other ones? Is it the connector that is different, battery voltage, size, or what exactly? Prices seems to be cheaper for newer models then older ones.

I know the voltage is different on a 701c but most others seem to be 3v? They all look like 2 wire systems so they are not being recharged by the motherboard correct?

[rkawakami]

Generally speaking, the CMOS (backup) batteries which come with their own attached wire/connector, differ only in the physical size (mainly thickness) and the connector that is used. The "button" or "coin" style batteries are regular 3V lithium (non-rechargeable) cells such as CR2032 (3.2mm thick) or CR2025 (2.5mm thick). The connectors are different between the 600 series and the T2x systems for example.

[GomJabbar]

You can buy CMOS batteries from various sources. While looking for an old post of mine I ran across a reference to the following site with good prices on these batteries. Note that I have not done business with them myself.
http://www.nicdladyonline.com/

Here is the post I wanted to show you.

A couple of years ago I wanted a CMOS backup battery for a model 600E ThinkPad. I went on IBM's website, and the price listed was about $420.00 as I recall. I sent IBM an e-mail saying there must be some error, as this is just a common coin cell with a short pair of wires and a plug. They responded that they would fix the price. I checked later, and the price was $15.00. I waited a few weeks to make the order, as I wanted to add a couple of items and I only wanted to pay one shipping charge (at the time $15.00 minimum). When I was ready to place the order, the price was again $420.00. I e-mailed IBM again, but this time I was told the price was correct, and it was based upon availability of the part. When availability became low, the price was adjusted accordingly. I guess there was no problem about IBM ever running out of a part Needless to say, I bought the CMOS backup battery elsewhere.

[Unknown_K]

So I got in 3 CMOS batteries for the T2x series ($1 each shipped). Replaced the connector with one from a 380xd and installed it (you just remove the pins from the new end connector and install them in the old connector using a needle to free them) and the 380XD now works (solved the issue with the BIOS reporting a dead fan too). The 380XD CMOS is a $6 ebay part compared to $1 for the newer T2x series (same 3V battery different end connector). The $1 batteries even came with the small pad of double sided tape so they stick instead of bouncing around.

What I would like to know is can a 701c thinkpad (1.2V CMOS) deal with a 3V battery, and is it a rechargable? If the unit can deal with 3V I can just use one of the spare new batteries instead of paying $12 + shipping. If the 701C is a rechargable I can just put a diode in line with the power lead so no voltage goes to the new battery (could blow up).

[RealBlackStuff]

No, it can't cope with 3V.
If you want to keep your 701c alive, you need to pay the price.
See also http://forum.thinkpads.com/viewtopic.php?f=6&t=81514