Looking for replacement CMOS/backup battery for T41 2378DHU

[hydrostarr]

My Thinkpad T41 2378DHU's BIOS clock has been resetting back to 1/1/1998 recently. This (seemingly) happens inconsistently when I've had my main battery removed after a hibernate (usually to switch the main battery).

What's a typical root cause for this? The CMOS/backup battery? Something else? (And why is IBM/Lenovo inconsistently naming this battery--CMOS vs. backup--and what's a "backup" battery mean? Just to backup the clock?) Is this is a common problem?

Fyi, I had been running EC 3.04 and BIOS 3.21 for a while; I upgraded to BIOS 3.23 just now.

I see the "backup battery" replacement requires quite an intrusive process:

http://www-307.ibm.com/pc/support/site. ... MIGR-52603

I'd like to try and avoid this.

Is there any means for me to check the health of this "backup battery," possibly with some diagnostic software?

Thanks in advance for any help,
-Matt

[Harryc]

Backup battery=CMOS battery. It sounds like you need a new one. It is really easy to replace. You just need to remove the keyboard (4 screws).

[rkawakami]

No software method exists to read/verify/check the status of the CMOS (aka, backup) battery as far as I know. The only thing you can do is remove and test it with a voltmeter. If less than about 2.7V, then it's basically toast. The purpose of the battery is to keep a small portion of the system's memory alive when main power has been removed (AC adapter and main battery). Said backup battery also keeps the real-time clock (RTC) running when main power is removed. The expected lifetime of such a battery is usually 5-7 years so yours may have died a little early. The T4x series places the battery in a spot which is not that easy to get to, as opposed to the T2x and 600-series which can be accessed by removing the main battery or an exterior access panel, for example. Some earlier systems also had backup batteries which required some disassembly.

[hydrostarr]

I'm having trouble finding many offerings for a backup/CMOS batter for an Thinkpad T4x series. The only 2 I can find are on ebay for $30:

http://cgi.ebay.com/Backup-Battery-14-1 ... dZViewItem

http://cgi.ebay.com/92P0986-Backup-Batt ... dZViewItem

At that price, I'll deal with occasional 5-minute bootups and reset of the bios clock.

Several other backup-battery flavors appear to be much less expensive:

http://search.ebay.com/search/search.dl ... category0=
http://www.nextag.com/thinkpad-cmos-battery/search-html

Might any of these be compatible with my T41 2378DHU?

[rkawakami]

According to the Hardware Maintenance Manual for the T41, the battery for a 14.1" system is FRU 92P0986. There are several on eBay at the moment which can be had for $10 or under.

http://search.ebay.com/ws/search/SaleSe ... le=92p0986

Note: search both title and description for this FRU number.

[GomJabbar]

Google the FRU number Ray gave and you should find a number of suppliers of this battery. I checked just now and got 854 hits.