Q: iPhone battery decreasing dramatically

Have you tried to do a full backup on iCloud or on iTunes with USB (remember to encrypt your backup so everything will be kept ! If not, some data will be lost!)

How to back up your devices using iCloud or iTunes - Apple Support

then do a complete restore, set your iPhone as a new device and see if it's till going on ?

How to erase your iOS device and then set it up as a new device or restore it from backups - Apple Support

If it does, try to contact Apple for this issue (if you iPhone is still under coverage)

My iPhone was having the same issue. I couldnt see anything while using it but with the Report I made with an Apple Advisor, he saw that some of my apps were opening and closing all the time. It was draining my battery.

The first thing to do is to ensure that it's not a software problem. Then, you can start resolving the hardware issue.

How did it went ?

I have 2 I phones 5s and a 6 plus and both since this last update are losing battery fast . It may be some app in the background but the only changes made to either phone in 2 weeks was this last update and they seem to die within a cpl of hours.  The phones did not do this before this last update.

I have the same problem and I already disconnected all apps to refresh and disconnected all notifications.. I mean it is at the point where the phone is becoming useless.... It was workign great prior to the last OS update! I did not even need to charge every day! Even with background apps running. Now, everything is turned off AND I need to charge twice a day! Ridiculous.

yeah.. the problem is the latest OS. Before that the phone was workign so great with all apps running in the background. Now, everything is turned off, messages are also turned off from email and FB, etc. I am at the point that the phone is no longer a phone... it will run out of battery mid sentence while talking IF on a rare occasion I get a phone call! It is your latest OS Apple! Please fix it!