Why a Mobile Phone Battery Has More Than Two Terminals?

Hi! If you are reading this then you must have been using a mobile phone for a very long time. But have you ever considered the fact that your mobile phone battery has more than two terminals? In this article, I am going to explain in detail Why a Mobile Phone Battery Has More Than Two Terminals.

Pins of 4 terminal battery
Pins of 4 terminal battery

Why a mobile phone battery is different?

Every battery we see around us has only two terminals. Like: a 9v battery, an inverter battery, a T.V remote battery, or any other kind of battery. Then why in the world a mobile phone battery has more than two terminals?

Different types of batteries
Different types of batteries

We all know that out of 3 terminals, two terminals of a mobile phone battery must be positive and negative respectively. Now, if it’s a three-terminal battery then its third terminal can either be BSI or BTEMP(Discussed below). And if it’s a four-terminal battery then the 3rd terminal is BSI and the fourth terminal is definitely BTEMP.

4 terminals of a Mobile phone battery
4 terminals of a Mobile phone battery

BSI PIN:

BSI stands for Battery System Indicator or Battery Status Indicator.

The work of this BSI pin is to give information such as the type and size of the battery to the mobile phone processor.

So when you plug in the mobile phone battery to your phone, this BSI pin automatically generates the signal which is received by the mobile processor.

This processor then determines the type and size or capacity of the battery which ultimately helps the processor to find out the voltage and current(mAh) of the battery.

Function of BSI Pin terminal
The function of the BSI Pin terminal

Another important function of this BSI pin is this: Let’s say you suddenly remove the battery from the mobile phone. Due to this BSI pin immediately interrupts and tells the processor to shut down all communications. Thus preventing damage to our data or mobile phone.

BSI pin prevents data loss
BSI pin prevents data loss

BTEMP Pin:

Battery temperature
Battery temperature

BTEMP stands for battery temperature.

As the name suggests, it gives information to the processor regarding the battery’s temperature.

This BSI pin is connected to a thermistor which is internally connected to a temperature sensor to prevent the battery and mobile phone in case the battery overheats.

What is a Thermistor in a battery?
What is a Thermistor in a battery?

Now if you are not familiar with a thermistor or how it works, below are the two images demonstrating how it works. So as the temperature around the thermistor changes so does its resistance.

At low temperature the resistance is high
At low temperatures the resistance is high
At high temperature the resistance is less
At high temperatures, the resistance is less

So yes you can say it kind of works like an LDR but an LDR OR Light Dependent Resistor changes its resistance according to the intensity of light that falls on it. Whereas a thermistor changes its resistance according to the temperature of its surroundings.

Difference between an LDR and Thermistor
Difference between an LDR and Thermistor

**Click here to read Automatic street light Project using LDR with Arduino

Hence BTEMP terminal actually gives information about the amount of charge remaining in the battery to the processor.

And this way, the BTEMP pin helps the processor in controlling the status and charging current of the battery. Thus ensuring a longer battery life of mobile phones.

Different battery levels

Conclusion

So with that being said, now whenever you will see a battery with 4 terminals you exactly know why it has more than two terminals:

For a 3-terminal battery: End terminals are positive and negative and the middle one is either BSI or BTEMP.

For a 4-terminal battery: End terminals are positive and negative and the middle ones are BSI and BTEMP.

Pins of 4 terminal battery

2 thoughts on “Why a Mobile Phone Battery Has More Than Two Terminals?”

  1. Hi: very interesting But some times you see a batter with 4 wires attached ? red + black – white ? yellow ? , Because the wires are covered up you don’t know which is the BSI AND BTEMP , am i right to say that the white is the BSI and yellow BTEMP ? , Also can you solder wires to a battery and use it for a device which has a connector block as long as the battery is the same voltage and the same mAh , I have a device which has the battery missing i know it’s is 3.7v 1100mAh and should have a 4 pin block attached with 4 wires red black white and yellow . So would it work ok in my device ? ( I have tried to get a new one for it but they are no longer available been looking for over 2 years ) .
    Thanks

    Reply

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