Cell phone battery voltage

[uday mehta]

today I checked my cellphone battery when it was nearly full charged. It showed 3.75 volt.
then I consume it till nearly discharge. it was still showing 3.74 voltage.
If voltage remain same then what get reduced?

and how mobile automatically understand the charging level(status) of battery. I mean there is no other power source to compare it then how it determine that now battery has fully charged or battery is going to discharge?

 

[Easyrider83]

Looks like you did measured something else. Fully charged Li-Ion battery should have a voltage about 4.15V per single cell.
And fully discharged is about 3.7-3.8V

 

[uday mehta]

then why it does not reduce to 0 volt ?
what is the meaning of fully discharged battery? minimum voltage, minimum current or something else?

 

[Surendhar M]

Certainly Your measurement was having some error. The battery status will be updated only by measuring the voltage level. So please recheck the level and let us know.

 

[Easyrider83]

Sure, you can discharge the battery to zero voltage, but it will greate chance to damage them. Usualy, minimum discharge level was protected by internal charging driver. Also the maximum voltage and current.

 

[Audioguru]

then why it does not reduce to 0 volt ?

Because it is not an old fashioned low capacity heavy Ni-Cad battery. Instead it is a Lithium battery that you can learn about at www.batteryuniversity.com .

What is the meaning of fully discharged battery? minimum voltage, minimum current or something else?

A fully discharged Lithium battery is 3.2V, if it discharges lower then it is badly damaged. So its low voltage is 3.2V and its fully charged voltage is 4.2V then its average voltage is 3.7V.

The cell phone knows the capacity of the battery it is supposed to use and it measures the amount of current during discharges. Then it calculates and shows what it thinks is the charge level of the battery.
A Lithium battery voltage quickly goes to the maximum charging voltage of 4.2V when charging but then it is only 70% fully charged so the voltage during charging does not accurately show the amount of charge.

 

[D.A.(Tony)Stewart]

Although the voltage reduces very little with State of Charge, except at the end, it does , enough to estimate SoC with a load. Thus it is nonlinear overall but linear from 20% to 80%.

Coulomb counters multiply I x t to compute charge used.

Load tests measure ESR which rises fast when SoC nears the end.