Battery Full [Q] BAtteryy Problemm

I charged my s2 plus to 100%.I work normally with it and when it goes to 15 % it drain fast to 1 %... I make calibration of battery but it doesn't work.I testet too when the battery was for example 70 % a get off battery from it and wait 2 min and when ia but it back it shows me 60%...Cann anybody know about this issues and tell me what to do???? and sorry for my poor english