Hey, I have the similar problem on my iPhone 6s. As I used it battery went weaker and weaker, I thought that's the common problem with Apple products so I went to the local repair shop and I changed battery. When I went home my battery was still weak and was draining fast. I thought that he didn't replaced it so I went to repair shop and he replaced it again, and the same problem. He change the connector port, and the same problem. My battery would die after 3 hours, and I always had my phone charged on. One day i left without my charger, and I got one from my friend, stuck it in my iPhone and that red icon was on, but it wasn't charging, and the battery completly drained out. I really can't afford more repairs, it already costed me more than 100$. I treid the home button and main button for a minute, nothing happens. I really need al the help from you guys. And for the record my iPhone never droped, or had any damage, never heated up, really don't know what should I do??