My battery dies very quickly on the iPhone 6, so much that I need an external battery pack.

Greetings. I have an iPhone 6, 16GB with the latest software updates installed. Recently I purchased an Apple Watch, and since then experience a rapid decrease in battery life with my iPhone. I have had to purchase an external battery pack to get even midway thru the day before the battery in both dies.

I have turned off most background running apps and limited location services. Aside from un-pairing the watch, which would defeat the purpose of having one, does anyone have some solutions they would be willing to share? Is there a site that I can go to that can run a diagnostic on the phone to see if it is another issue entirely?

Thank you, I look forward to your responses.