IBM ThinkPad X20 Hardware Maintenance Manual page 41

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 the reinstalled battery pack has not been charged,
go to the next section.
Checking the battery pack: Battery charging does not
start until the Fuel Gauge shows that less than 95% 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.
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 4 (-). See the
following figure:
Terminal
1
4
3. If the voltage is less than +11.0 V dc, the battery pack
has been discharged.
4. If the voltage is more than +11.0 V dc, measure the
resistance between battery terminals 3 and 4. The
resistance between battery terminals 3 and 4 must be
from 4 to 30k ohms.
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.
Checking the backup battery: Do the following:
1. Power off the computer, and unplug the AC adapter
from it.
4(-)
Voltage (V dc)
+ 0 to + 12.6 (6-cell) +0 to 16.8(4-cell)
Ground (-)
Chapter 2. General descriptions
1(+)
2
3
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