Why a Mobile Phone Battery Has More Than Two Terminals?

Hello viewers! 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? If not, then this is probably the best techy. article on this topic for you because we are going to go deep to find out Why a Mobile Phone Battery Has More Than Two Terminals?.

Why a Mobile Phone Battery Has More Than Two Terminals?


Now why this question is so curious in the first place?

Well because every battery we see around us has only two terminals whether it’s 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?



We all know that out of 3 terminals, two terminals of a mobile phone battery are: 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 will be BSI and fourth terminal will definitely be BTEMP.




BSI stands for Battery System Indicator or Battery Status Indicator. The work of this BSI pin is to give information like type and size of the battery to 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. Then Processor 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.



Another important function of this BSI pin is this: Let’s say you suddenly remove the battery from 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.







BTEMP stands for battery temperature. As the name itself suggest it gives the information to the processor regarding 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 battery overheats.



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 thermistor changes so do its resistance.

at low temperature resistance is high
at low-temperature resistance is high
at high temperature resistance is less
at high-temperature resistance is less


So yes you can say it kind of work 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


Hence BTEMP terminal actually gives information of the amount of charge remaining in the battery to the processor. In this way, BTEMP pin helps the processor to control status and charging current of battery and thus ensuring a longer battery life of mobile phones.



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.


  1. Hello There. I found your blog using msn. This is an extremely well written article. I’ll be sure to bookmark it and return to read more of your useful information. Thanks for the post. I’ll definitely comeback.

  2. Nice read, I just passed this onto a colleague who was doing a little research on that. And he actually bought me lunch as I found it for him smile Therefore let me rephrase that: Thanks for lunch!

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