Battery problem?

My iPhone 6 is only a year and five months old and lately I noticed that the battery had been draining way faster than normal. In the last couple of weeks it would randomly shut off when I opened snapchat, I thought that maybe I should just update snapchat, so I did. Well now if I open any of my apps my phone turns off and it won't let me turn it back on because it says the battery is low, yet when I plug in my phone to charge, it will be have battery and the phone just shut off for no reason. Sometimes all it takes is me plugging it back in for a minute or so for it to turn back on, but it turns off again shortly after. Today if my stayed on 100% for a good part of the morning so I'd hoped that maybe the problem was fixed, but once it got under 80% battery and I opened an app, it would shut off. It happens several times throughout the day, has anyone else had this problem?