Why does the new update affect the battery life?

My IPhone 6 has never had any issued with battery life until this latest update. Please don't go in and tell me to turn things off etc. Nothing has changed on my phone except I accepted the latest update and now I can't have my battery last a full day and that is only checking Facebook and emails. I am not using the mapping or even listening to music.

I also have a Fitbit and a previous update on the Fitbit caused it to do the same thing. It seems like you and the Fitbit community are trying to get people to get off of the older devices and upgrade to newer ones.