# Why does this mobile phone battery have 4 terminals? [duplicate]

Why do some mobile phone batteries have 4 terminals? I want to use a mobile phone battery for my project.

• i think one is for temperature sensing – BASIL VARGHESE Feb 27 '14 at 4:35
• The circle in your image covers up the labels for the terminals. Assuming that the missing label is -, the other two could be for Temperature, Data, or something else. – jpaugh Dec 3 '16 at 18:49

## 2 Answers

The pinouts of phone batteries are different between all types. You can almost see these pinouts in many cases: All About Battery connector pinout of mobile phone and also maybe this link will help you: Why are there 3 pins on some batteries?

• I think this is the correct answer - no way to tell for sure. I've looked at various forums online and there is no consensus. Some of them are thermistors, others are ID pins for identifying the type of battery (based on resistance), or I2C (pair of pins), and still others are 1-wire comms. My Samsung battery, for example, is 4-terminal, with 3 of the terminals labeled -, T, and +. The middle is apparently a thermistor, making the fourth a 1-wire bus (to support NFC). – Chris Laplante Feb 27 '14 at 5:10

I think two of the pins are (-) for the battery + protection circuit, one is for the (+) of the battery + protection circuit, and the fourth is for a 10K thermistor to the (-) side. See this compatible battery image. T = Thermistor.

It would be easy enough to probe out with a multimeter (check that volts are zero before trying to measure ohms).