My Samsung S3 battery - shows some residual power even after the battery drains completely. Is this normal?

[AC Question]

samsung s3 battery - shows some residual power even after the battery drains completely

my samsung s3 battery is behaving funny for the last few weeks . after charging 100 % in the morning , it will run for 6-8 hrs and then it will turn off due to no charge in the battery/battery drain. when i try to charge it , the mobile shows 38 % on the battery ( when I attach the charger ) and will start charging from there instaed of 0 % . i am confused .....

 

[Rukbat]

Re: samsung s3 battery - shows some residual power even after the battery drains completely

The way State of Charge is measured is to measure the voltage at the battery's terminals. Since the charger voltage has to be higher than the battery voltage, the State of Charge is going to be inaccurate until the battery is fully charged and charging stops. So that "38%" could be 20%, which is where most phones shut off. The phone won't let you drain the battery to complete 0, because it takes a specialized charger to charge a fully discharged lithium battery. (They're built partially charged.)

If it used to show 0%, the calibration is off, and an app like Battery Calibration (Root) (the phone has to be rooted to change the calibration curve) might help. (The "100%" indication is also inaccurate - the battery is fully charged when the voltage at the terminals - to 3 decimal places - stops rising during charging for at least one minute. [That's as close as we can get without tearing the battery apart and measuring the chemicals in it.])