Checking Operational Charging; Checking The Battery Pack; Checking The Backup Battery - Lenovo ThinkPad T420s Hardware Maintenance Manual

Checking operational charging

To check whether the battery charges properly during operation, use a discharged battery pack or a battery
pack that has less than 50% of the total power remaining when installed in the computer.
Perform operational charging. If the battery status indicator or icon does not turn on, remove the battery
pack and let it return to room temperature. Reinstall the battery pack. If the charge indicator or icon still does
not turn on, replace the battery pack.
If the charge indicator still does not turn on, replace the system board. Then reinstall the battery pack. If it is
still not charged, go to the next section.

Checking the battery pack

Battery charging does not start until the Power Manager Battery Gauge shows that less than 96% of the
total power remains; under this condition the battery pack can charge to 100% of its capacity. This protects
the battery pack from being overcharged or from having a shortened life.
To check your battery, move your cursor to the Power Manager Battery Gauge icon in the icon tray of the
Windows taskbar and wait for a moment (but do not click), and the percentage of battery power remaining
is displayed. To get detailed information about the battery, double-click the Power Manager Battery
Gauge icon.
Note: If the battery pack becomes hot, it may not be able to charge. Remove it from the computer and leave
it at room temperature for a while. After it cools down, reinstall and recharge it.
To check the battery pack, do the following:
1. Power off the computer.
2. Remove the battery pack and measure the voltage between battery terminals 1 (+) and 7 (-). See the
following figure:
3. If the voltage is less than +11.0 V dc, the battery pack has been discharged.
Note: Recharging will take at least 3 hours, even if the indicator does not turn on.
If the voltage is still less than +11.0 V dc after recharging, replace the battery.
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 adapter from it.
2. Turn the computer upside down.
3. Remove the battery pack (see "1010 Battery pack" on page 68).
4. Remove the backup battery (see "1090 Backup battery" on page 83).
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7(-)
6(-)
5
3 4
2(+)
1(+)
Terminal Voltage (V dc)
1 + 0 to + 12.6
7 Ground (-)