Original post by: Brian Wood ,
Is your battery still original or has it ever been replaced? I have noticed that iPhone 6 and up batteries are dying at rates much higher than the 4 and 5 series iPhones. I've replaced more iPhone 6s batteries than any other model and all were original batteries. It's either an issue with the batteries themselves or maybe charging habits. I'd replace the battery with an iFixit battery replacement part, if you haven't replaced the battery already.