iPhone 12mini overnight battery drain issue facing

I am using iPhone 12mini recent times I noticed overnight battery drain issue I am facing its automatically decreasing my battery percentage I found that issue was made by signal 4g when I turn to 3G it’s Norma in night no drain issue but when I am put in 3G no service shown please fix this as soon as possible thanq so many members are facing please make it fast thanq u r lovely iPhone user