Battery problem

[AC Question]

Hello! I have the lenovo A536. The last 2 years everything was ok with it. I have been using diffrent custom marshmallow roms, but last week i flashed a new nougat rom and i noticed that the battery was draining with the speed of light. I readed somewhere that it may need a calibration so i did it but nothing changed. I decided to restore a backup of my old 6.0 rom but the problem was still there. So I decided to wipe the rom and flash it again. But the battery was still draining very fast. I tried with another battery for A536 and it was too draining very very fast. Looks like the problem is in the phone, not the battery. Idk what to do. Pls help me