> The phone also dies with 40% battery! I turn it on, it shows a splash screen meaning low battery, turns on, shows 40% battery, then dies after a moment again.Funny thing is that I try restarting it several times and at some point it starts working for hours (which means it actually does have 40% battery and its not a calibration issue).

Other complaints aside, have you considered that your device might be defective? What you describe is neither common nor accepted by iPhone users at large.