Lenovo ThinkPad P51 Hardware Maintenance Manual page 34

3. Measure the voltage of the coin-cell battery. See the following illustration.
• If the voltage is correct, replace the system board.
• If the voltage is not correct, replace the coin-cell battery.
• If the coin-cell battery discharges quickly after replacement, replace the system board.
28
ThinkPad P51 Hardware Maintenance Manual
Wire Voltage (V dc)
Red +2.5 to +3.2
Black Ground