My phone quickly loses its charge even after replacing the battery

Almost overnight, my iphone 6s has stopped holding a charge like it did before. For example, if it is not at 100 percent when I go to bed, it will die by the morning. It drops percentage even when not in use. I checked the battery health and it was 83 percent, so I used ifixit to get a new battery and replace it. It shows battery health at 100 percent since I have replaced it, but it still loses its charge very quickly. I have to plug it in several times a day to keep it from dying.