Why the battery in some mobile phones after some time stars to discharge faster?

[iMore Question]

Because you have to charge your battery,it have to write on your mobile phone full battery,and when you get new mobile phone you have to discharge all battery and then charge battery 12 hours

 

[kch50428]

Nature of the beast as batteries go... They have a finite number of charge/discharge cycles, and there comes a point in their life when they can't charge fully anymore, and drain faster.