Lenovo ThinkPad X300, Hardware Maintenance Manual

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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 60).
4. Remove the backup battery (see “1090 Backup battery” on page 77).
5. Measure the voltage of the backup battery. See the following figure.
Red (+)
Black (-)
Wire Voltage (V dc)
Red +2.5 to +3.2
Black 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.
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