Battery Low [Q] Battery drain when it's less than 40%

Hi. I'm having a big problem with my Galaxy SII GT-I9100. It works normally till the battery percentage gets 40%. After that the phone starts to slow down, screen starts blinking, signal gets lost and at last it turns off. All these happen in a few seconds' time. These are what I did:
1.Changed battery 2 times
2.Calibrated battery with 3-4 apps from play market
3.Wiped everything that's possible. Tried using NeatROM, Revolution , Carbon roms.
4.Took phone to master and realized that he knows less than me.
After all these procedures anything has changed. Please help me solving this problem.