Why Cell Phone Battery Has 3 Terminals?

Why cell phone battery has 3 terminals? Or does your one have 4?

The cell phone battery has a temperature sensor pin to prevent overheating. It also includes a BSI pin in the middle. But what is the purpose of those extra pins? Find out below!

You may have already noticed the extra terminals in your cell phone battery. After reading this article, check out how many terminals your phone battery has if not yet. It possibly has three or more batteries. But what is the point of those extra terminals? We will discuss it in this article. Read throughout it to know more if you are a battery enthusiast.

why cell phone battery has 3 terminals

Why Cell Phone Battery Has 3 Terminals?

All our known standard batteries have two terminals. Your car battery, lawn tractor battery, air conditioner or TV remote battery, inverter battery, these batteries only have two terminals. But things get different when you check your phone battery. It either has three or four terminals. The reason behind this is that your phone battery is designed differently than other batteries. And the extra terminals are there for performing the phone tasks smoothly. Whether the phone battery has three or four terminals, two of them are basic terminals- positive terminal and negative terminal.

Whether your cell has three or four terminals, they are there for a reason. Each terminal has its own job to perform. In cell phones, manufacturers use various types of Lithium Polymer batteries for their power storing capacity. If your phone battery has four terminals, then a possible assortment would be-

First Terminal: Positive Terminal

Like the regular battery, cell phone batteries have a positive terminal. It is one of the common points in a three or four-port cell phone battery.

Last Terminal: Negative Terminal

The cell batteries have a negative terminal like any normal battery. In a three or four terminal cell battery, one common terminal is the negative terminal.

Third Terminal: BTemp or Internal Thermistor

The third terminal might be positioned between the positive and negative terminal. This extra terminal is generally an internal thermometer. The thermometer, like any thermostat, measures the temperature, but it measures the internal temperature of the cell phone. A cell phone has intricate circuits. When they come near excess heat, the circuits may get burnt or damaged. The BTemp or battery temperature pin sends information regarding the battery temperature to the cell phone processor.

A thermistor or internal temperature sensor keeps the battery from overheating. When you charge a phone, due to many reasons, it can overheat. The battery can heat up as well. Terminal connectors connect two terminals. The BTemp pin connects the battery to an internal sensor that sends a signal to the processor if the battery heats up. A thermistor develops higher resistance when contacted with heat. 

Fourth Terminal: BSI or Battery Status Indicator

And if your cell phone battery has four terminals, what is the fourth terminal supposed to do? 

When any phone battery includes four terminals, the other terminal can be BSI or battery status indicator. It is also known as the battery system indicator. This indicator prevents any communication when the battery is not attached to the phone. It gives a signal to the processor to stop doing the functions when suddenly the battery is removed. This way, the system helps to prevent damaging the device or the data saved in it.

Besides that, BSI connects the battery to the phone’s processor. The processor identifies the battery type and size through that pin. That way, the cell phone processor controls other vital tasks related to the battery using that pin’s information. Also, it helps the processor to identify the capacity, that is, the voltage and current of the battery. Therefore, you get to know the mAh or Milliamp Hour.


Why Are There 3 Wires on a Battery?

In cell phone batteries, there might be three battery wires which are different from regular batteries. There is an extra pin on the battery that is either the BSI (Battery Status Indicator) or the BTemp (battery temperature sensor).

What Is the Middle Terminal on a Phone Battery?

In a phone battery, there are usually three pins or terminals. The first and last terminal is the positive and negative terminal. In the middle, the terminal can either be a temperature sensor or battery status indicator. It solely depends on the manufacturer which pin did they put in the middle terminal.

Why Do Cell Phone Batteries Have 4 Pins?

Cell phone batteries are a little different from regular batteries. The fourth pin indicates- positive, negative, BSI, and temperature sensor. The positive and negative terminals are there for general recharging purposes. And the battery status indicator identifies battery type, size, and voltage requirement for that battery. Lastly, the temperature sensor prevents overheating.

What Are the Terminals of a Cell Phone Battery?

Generally, a cell phone battery may have three or four terminals. The battery terminals are as below-

i) Positive Terminal

ii) Negative Terminal

iii) BSI or Battery Status Indicator

iv) BTemp or Battery Temperature Sensor

The first two terminals are common in car batteries. But the loose battery terminals might make the device stop working as they do in cars.

Why Are There Three Pins on Some Batteries?

There might be three pins on some phone batteries. The first two pins are positive and negative terminals. The third pin is there to measure the temperature. In cell phone batteries, the third pin generally works as an internal temperature controller. The middle terminal indicates the temperature of the battery when charging. It could also be a battery status indicator or BSI.


Why cell phone battery has 3 terminals? Cell phone batteries have one or two extra pins for temperature control and battery status indication. When the battery is charging, it may get heated. So, the temperature controller pin sends a signal to the processor and prevents overheating. The status indicator also plays a significant role by identifying and informing battery-related information to the cell phone processor.

Featured image credit: wikiwand.com

Hi! I'm Liam Oscar, and this is where I spend most of my time attempting to publish valuable articles for my readers! This site contains all of the information that I believe we all need to know about batteries, chargers, and other accessories.

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