Checking The Backup Battery - Lenovo ThinkPad Edge E420 Hardware Maintenance Manual

4. If the voltage is more than +11.0 V dc, measure the resistance between battery terminals 5 and 7.
The resistance must be 4 to 30 K Ω. If the resistance is not correct, replace the battery pack. If the
resistance is correct, replace the system board.

Checking the backup battery

Do the following:
1. Power off the computer, and unplug the ac power adapter from it.
2. Turn the computer upside down.
3. Remove the battery pack (see "1010 Battery pack" on page 56).
4. Remove the backup battery (see "1090 Backup battery" on page 66).
5. Measure the voltage of the backup battery. See the following figure.
• If the voltage is correct, replace the system board.
• If the voltage is not correct, replace the backup battery.
• If the backup battery discharges quickly after replacement, replace the system board.
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Hardware Maintenance Manual
Wire
Voltage (V dc)
Red +2.5 to +3.2
Black Ground