R40 CMOS battery

[RealBlackStuff]

As most owners of an R40 (should) know, their CMOS battery looks different from the rest of the IBM CMOS batteries.
The R40 has a black heatshrink tube around it, and all the others are yellow.
The batteries themselves are both the same (CR2032 3V) but the venom is in the connections!

The + and - on the R40 battery plug are just the opposite way of yellow ones.
You can use a yellow battery in an R40, if you just swap the pins around.

Ray Kawakami has some good pictures of this here:
http://forum.thinkpads.com/viewtopic.php?f=18&t=90787

[misfit]

Thanks RBS, that's handy to know.

[eddief]

I also have a Thinkpad R40 with a possibly bad backup battery.

If the R40 was not plugged in, on booting it says something like the CMOS is corrupt. I boot into the BIOS, select default values and set the date and time - then the R40 is OK as long as I keep it plugged in while it is off.

The existing battery measured 2.77 volts.

I bought a replacement battery off of Ebay for $1.55. I recieved it in a few days. I decided to test the voltage of the batter before I plugged it in but to my surprise it measures 3.48 volts!

3.48V is 16% above 3V. Supposedly +/- 10% is acceptable. That would be 3.3V.

Is it safe to plug in a 3.48V battery??????????????

As most owners of an R40 (should) know, their CMOS battery looks different from the rest of the IBM CMOS batteries.
The R40 has a black heatshrink tube around it, and all the others are yellow.
The batteries themselves are both the same (CR2032 3V) but the venom is in the connections!

The + and - on the R40 battery plug are just the opposite way of yellow ones.
You can use a yellow battery in an R40, if you just swap the pins around.

Ray Kawakami has some good pictures of this here:
http://forum.thinkpads.com/viewtopic.php?f=18&t=90787

[misfit]

I also have a Thinkpad R40 with a possibly bad backup battery.

If the R40 was not plugged in, on booting it says something like the CMOS is corrupt. I boot into the BIOS, select default values and set the date and time - then the R40 is OK as long as I keep it plugged in while it is off.

The existing battery measured 2.77 volts.

I bought a replacement battery off of Ebay for $1.55. I recieved it in a few days. I decided to test the voltage of the batter before I plugged it in but to my surprise it measures 3.48 volts!

3.48V is 16% above 3V. Supposedly +/- 10% is acceptable. That would be 3.3V.

Is it safe to plug in a 3.48V battery??????????????

Yes, that should be fine (as long as you have the polarity correct). 3.48V is 'no-load' and not uncommon for a new CMOS cell. I just tested a new Energiser CR2032 I have here and it's 3.36V. The old one at 2.77 no-load would have dropped to under 2.5 under load.

If it worries you discharge the new cell a bit, the voltage will likely drop then.

[eddief]

Just wanted to update this thread.

I plugged in the the battery I got from Ebay, noload 3.48V, and after the manditory swapping of the battery leads at the connector on the battery the machine runs perfectly. The date and time are always good, machine begins to boot XP within a second.