I have a 6s plus, and had the battery replaced, and still drains the battery like that. I’ve tried all the obvious tricks. I’m befuddled by this, it’s the worst

I have a 6s plus, and had the battery replaced, and still drains the battery like that. I’ve tried all the obvious tricks. I’m befuddled by this, it’s the worst battery life of any phone I’ve had. I thought the bigger case would have helped, but maybe the bigger screen out weighs it. What I find mystifying is why as an average user it’s impossible to figure out why it happens, is it normal, is your phone broken? Apple docs and support provide no insight into one of the primary usability issues. Other than that, it’s quite a nice phone. I picked it up cheap on Craigslist and it’s going strong for two years.