The week I got my OnePlue One phone I was too busy to do the full transfer of apps and data from my old phone, so I just played with it from time to time, but largely just left it alone. The battery life was amazing on stand-by, connected to WiFi. It practically lasted the week without charge. Great, I thought.
Then this week, I finally got around to installing my most commonly used apps. After I did this though, battery life went through the floor. The phone was awake all the time, as shown in the standard battery stats. It just wouldn't go to sleep. The OnePlus One had insomnia.
I tried uninstalling some apps that I thought might be causing the issue. Looking at the battery consumed by each app, the Google Play Services (GPlayS) process seem to be the culprit, but that was not the case during the first week. So it was mostly likely an app I had installed that was making lots of requests to GPlayS.
I got bored of uninstalling apps, one by one, and checking whether the phone's insomnia was cured. So I decided to factory reset the phone and start again. Only this time I would install one app at a time and check to make sure the phone was sleeping after each install.
One thing I also did that day when I installed a load of apps was to set the default SMS to Google Hangouts. I'm now wondering if that was indeed the problem. Hangouts will have deep hooks into GPlayS I bet. So I've decided not to do that this time. I'll keep SMS to the default SMS app.
So far I've installed Google Inbox, Three inTouch (WiFi calling app), Google Fit, and the phone is sleeping fine. I will update this post if I do find the ultimate culprit.