IBM ThinkPad 340 Series Hardware Maintenance Manual page 222

If the backup battery discharges quickly after
replacement, replace the system board.
Checking the Standby Battery
1. Power-off the computer and unplug the AC Adapter
from the computer.
2. Open the keyboard, and remove the battery pack and
the diskette drive.
3. Remove the standby battery.
4. Measure the voltage of the standby battery.
If the voltage between red and black is 3.5 V dc
or greater, the voltage is correct. Go to Step 10
on page 213 to verify standby battery operation.
If the voltage is less than 3.5 V dc, go to the
next step.
5. Plug the AC Adapter into the computer and power-on
the computer.
6. Measure the output voltage at the connector on the
system board.
Black
Pin
+
−
If the voltage is less than +4.0 V dc, replace the
DC/DC card. If the voltage is still low, replace
the system board.
If the voltage is more than +4.0 V dc, power-off
the computer, replace the standby battery, and
go to the next step.
7. Ensure that the AC Adapter is plugged into the
computer; then power-on the computer.
212
IBM Mobile Systems HMM
Red
Voltage (V dc)
+4.0
Ground