Jim Hamm recently experienced an unusual battery drain on his iPhone, running iOS 9. He read the following article, and made several changes in various settings. He found the culprit for his heavy battery use -- an app "ClockRadio". He does not use this app, and recently turned it on just to see what it was all about. Unknown to him, once opened it started a lot of background activity, which consumes battery power. He shut it down, and hopefully it won't do any more background activity.
The following article gives some helpful tips on improving battery life on your iPad or iPhone.