Apple Smart Battery Case iPhone 11 Pro Max

Does the Apple Smart Battery case cause the battery in the iPhone to degrade faster? Is it safe to use? Also I have heard that when the case is connected it utilizes the battery from the case first then it begins to draw from the iPhone when the case is depleted. However since I have connected the case my battery on my iPhone always presents as charging. Is this also normal and now my concern is that I’m doing more harm than good by using the case.