ThinkPad T420 - Checking the Battery Pack; Checking the Backup Battery

Performoperationalcharging.Ifthebatterystatusindicatororicondoesnotturnon,removethebattery
packandletitreturntoroomtemperature.Reinstallthebatterypack.Ifthechargeindicatororiconstilldoes
notturnon,replacethebatterypack.
Ifthechargeindicatorstilldoesnotturnon,replacethesystemboard.Thenreinstallthebatterypack.Ifitis
stillnotcharged,gotothenextsection.
Checkingthebatterypack
BatterychargingdoesnotstartuntilthePowerManagerBatteryGaugeshowsthatlessthan96%ofthe
totalpowerremains;underthisconditionthebatterypackcanchargeto100%ofitscapacity.Thisprotects
thebatterypackfrombeingoverchargedorfromhavingashortenedlife.
Tocheckyourbattery,moveyourcursortothePowerManagerBatteryGaugeiconintheicontrayofthe
Windowstaskbarandwaitforamoment(butdonotclick),andthepercentageofbatterypowerremaining
isdisplayed.Togetdetailedinformationaboutthebattery,double-clickthePowerManagerBattery
Gaugeicon.
Note:Ifthebatterypackbecomeshot,itmaynotbeabletocharge.Removeitfromthecomputerandleave
itatroomtemperatureforawhile.Afteritcoolsdown,reinstallandrechargeit.
Tocheckthebatterypack,dothefollowing:
1.Poweroffthecomputer.
2.Removethebatterypackandmeasurethevoltagebetweenbatteryterminals1(+)and7(-).Seethe
followinggure:
Terminal
Voltage(Vdc)
1+0to+16.8
7
Ground(-)
1(+)
2(+)
3
4
5
6(-)
7(-)
3.Ifthevoltageislessthan+11.0Vdc,thebatterypackhasbeendischarged.
Note:Rechargingwilltakeatleast3hours,eveniftheindicatordoesnotturnon.
Ifthevoltageisstilllessthan+11.0Vdcafterrecharging,replacethebattery.
4.Ifthevoltageismorethan+11.0Vdc,measuretheresistancebetweenbatteryterminals5and7.
Theresistancemustbe4to30KΩ.Iftheresistanceisnotcorrect,replacethebatterypack.Ifthe
resistanceiscorrect,replacethesystemboard.
Checkingthebackupbattery
Dothefollowing:
1.Poweroffthecomputer,andunplugtheacpoweradapterfromit.
2.Turnthecomputerupsidedown.
3.Removethebatterypack(see“1010Batterypack”onpage67).
4.Removethebackupbattery(see“1100Backupbattery”onpage83).
5.Measurethevoltageofthebackupbattery.Seethefollowinggure.
38ThinkPadT420andT420iHardwareMaintenanceManual
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