IBM ThinkPad R40 2681 - Checking the Backup Battery

If the resistance is not correct, replace the battery
pack. If the resistance is correct, replace the system
board.
Checking the backup battery
Do the following:
1. Power off the computer, and unplug the ac adapter
from it.
2. Turn the computer upside down.
3. Remove the battery pack (see “1010 Battery pack” on
page 64).
4. Remove the backup battery (see “Checking the battery
pack” on page 40).
5. Measure the voltage of the backup battery. See the
following figure.
Red(+)
Blue(-)
Wire Voltage (V dc)
Red +2.5 to +3.2
Blue Ground
v If the voltage is correct, replace the system board.
v If the voltage is not correct, replace the backup battery.
v If the backup battery discharges quickly after
replacement, replace the system board.
Checkout guide
42 ThinkPad R40