Checking The Backup Battery - Lenovo ThinkPad T400s Hardware Maintenance Manual

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 85).
4. Remove the backup battery (see "1080 Backup battery" on page 102).
5. Measure the voltage of the backup battery. See the following figure.
Red (+)
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.
Black (-)
Wire Voltage (V dc)
Red +2.5 to +3.2
Black Ground
53
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