wrote:
Hi,

I have an old IBM Thinkpad T23 laptop computer. Recently, I have
trouble with the display, black, when I first power up the laptop. After
WinXP boots up, I hold down the Fn key and press F7 (int/ext display)
key to get the display turned on. I often have to do this more than once.

Note: I recently replaced the CMOS battery. I changed the BIOS
(press F1 at power up) setting for "boot display" from "both" to "LCD".

I SAVED the change, but the next time I boot up the T23, I have
the same issue. I reboot the T23 and press F1. BIOS settings, the
boot display is back to "both".

Does anyone know why WinXP changes the BIOS setting?

Thank You in advance, John

My guess is, the T23 doesn't have a working main battery pack
installed in it. When you shut down Windows at the end of the day,
you likely unplug the adapter that is powering the T23 all
the time. This causes the RTC to run off the CR2032 coin cell
until the next morning.

For at least the BIOS setting, the CMOS RAM used for the setting
is battery-backed. If the CR2032 is flat, the CMOS settings
won't be maintained and the next morning when you plug in
the main adapter (as a surrogate for the missing battery pack),
the tiny CMOS power cell has not done its job, and so your
correction to the BIOS yesterday is being lost.

You'll need to find a manual or a takeapart, to identify where
the tethered coin cell is located. It has a tiny two-pin connector
on the end. There should be a pin header where it plugs in. The
CMOS cell likely has the wires on the battery end "cold welded"
to the metal surface. Then, they put that plastic pouch around it,
so that the conductors don't touch anything when the CMOS battery
is inside the laptop.

https://www.amazon.ca/DBTLAP-Compati.../dp/B07QTGNF4S

The battery is 3.0V or so when new. The Southbridge CMOS well minimum
voltage is 2.0V. A series diode with a forward drop of 0.3V prevents
current from flowing into that battery. So the minimum measured value
at the (+) terminal on the CMOS battery would be 2.3V or so. The CR2032
lasts for around 3 years, if no main battery pack is present to hold
up the load. The main battery pack would be contributing to the
electrical circuit if it was present. When the main battery pack
is missing, you use the laptop 8 hours a day, and 16 hours of the
day the CR2032 powers the RTC/CMOS, then the coin cell lasts
for about 3 years.

There are actually two kinds of coin cells. There are also rechargable
coin cells, similar in shape to the non-rechargable CR2032. You have
to be careful to replace "like-with-like". A CR2032 should definitely
not be used in place of the rechargable coin cell type, as the CR2032
is not rated for charging and it will swell up if charged.

https://en.wikipedia.org/wiki/Button_cell

"Rechargeable batteries typically have the same dimension-based numeric
code with different letters; thus CR2032 is a disposable battery while
ML2032, VL2032 and LIR2032 are rechargeables that fit in the same holder
if not fitted with solder tags. It is mechanically possible, though
hazardous, to fit a disposable battery in a holder intended for a
rechargeable; holders are fitted in parts of equipment only accessible
by service personnel in such cases."

You would replace the CR2032 with another CR2032.

*******

That doesn't say anything about how things work in Windows XP.

It's a guess at symptoms in your BIOS-level description. And
it's my guess the CR2032 has conked out, and with no main
battery pack to assist, it's the guilty party. The BIOS level
settings are now getting lost due to a lack of powering
(dead CR2032, no main battery pack).

Paul