How Cell Phone Batteries Calculate Remaining Charge

[vivekrai]

I do not know to which section this question belongs correctly.

The question is :

How does our cellphone calculates or knows the percentage of battery left?

 

[Bobbywhy]

A typical cell phone battery is the lithium-ion type. It is fully charged when the battery open circuit voltage is around 4 volts. As energy is used the voltage drops off towards around 3.5 volts. This 0.5 volt change corresponds to going from fully charged 100% to around 20%. Somewhere just below 3.5 volts the unit will reach “low battery” and turn off automatically. The state-of-charge monitor circuit of the cell phone simply measures the battery voltage and indicates to the user by means of a display of “percent charge remaining”, often with a bar graph.

http://batteryuniversity.com/learn/article/lithium_based_batteries

 

[Borek]

More or less by measuring exact voltage and applying the http://en.wikipedia.org/wiki/Nernst_equation

 

[Topher925]

Voltage measurement (at least voltage measurement alone) is rarely used for determining Li battery SOC. This is due to modern Li batteries having relatively flat voltage curves as they are discharge along with the voltage being dependent upon battery temperature, health, and life, as well as SOC. The most common method used is coulomb counting where the current discharged from the battery is integrated over time starting from a full charge.

True SOC of a Li battery is actually a very very difficult thing to determine and is a huge engineering challenge for automotive and similar applications.

 

[alphy]

I can explain the process by which cell phone batteries calculate remaining charge. Cell phones use a type of battery called a lithium-ion battery, which contains a microchip that monitors the battery's voltage and current. This microchip is called a battery management system (BMS) and it uses a process called coulomb counting to estimate the remaining charge.

Coulomb counting is a method of measuring the amount of charge that has been added or removed from a battery. The BMS keeps track of the amount of charge that goes into the battery when it is charging and the amount of charge that comes out of the battery when it is being used. By continuously monitoring this charge, the BMS can estimate the remaining charge in the battery.

Additionally, cell phones use a technique called voltage monitoring to calculate remaining charge. This method involves measuring the voltage of the battery and comparing it to a known voltage curve. As the battery is used, the voltage decreases and the BMS can use this information to estimate how much charge is left.

In some cases, cell phones may also use a combination of coulomb counting and voltage monitoring to calculate remaining charge. This allows for a more accurate estimation, as voltage monitoring alone can be affected by temperature and other factors.

Overall, the BMS in cell phone batteries uses complex algorithms and data from coulomb counting and voltage monitoring to calculate the remaining charge. This information is then displayed as a percentage on the cell phone's screen.