IBM ThinkPad A21m Hardware Maintenance Manual page 44

3. Remove the battery pack (see "1010 Battery pack" on
page 60 ).
4. Remove the backup battery (see "Checking the battery
pack" on page 37).
5. Measure the voltage of the backup battery. See the
following figure.
Red (+)
Black (-)
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.
38
ThinkPad A20m/p, A21m/p, A22m/p
Wire Voltage (V dc)
Red +2.5 to +3.2
Black Ground
Checkout guide