No, there is absolutely no sense behind such claims that battery cases ruin iPhone battery. Instead, the factor that determines the degradation of the iPhone battery is its charging cycle. In short, it depends upon how many cycles of charging the battery has gone through.  It also relies on the number of hours one uses the smartphone. Hence, it is absolute nonsense to claim that smart battery cases over the iPhones damage its battery. Instead, it provides greater detail about charging. Naturally, one can avoid the instances of over and undercharge. Above all, it assures more excellent safety of the device as well.