why Mobile Battery's have 3 pins

[bippi]

in a common battery there is only 2 pin (one for +'ve and other for -'ve) but when in the case of mobile phones battery there seem 2 pins why it is so what is the need for the 3rd one? and its use. and how we find the pins (ie. is there is any order for the arrangement of pins.)


Thanks in advance...

 

[Asus_USA]

Positive, Negative, and DATA (to communicate with the phone/device).

 

[bippi]

Positive, Negative, and DATA (to communicate with the phone/device).

would you please explain more what type of communication and how it is arrange is it in +'ve - data - -'ve and how to recognize each. and how the communication possible with no circuit or sensors..