This morning my phone battery has dropped from 100% to 85% overnight, while in airplane mode. I poked around and got this information out of the OS and BetterBatteryStats. It looks like nlpwakelock is using the battery - NLP is network location provider, a google service. It doesn't do it every night.
I've turned off location tracking/history in google maps, and based on a bit of googling and found the play store can cause issues, so I uninstalled updates and it's back to an earlier version. I've heard of an app called "greenify" which may mitigate the problem, but I'd rather figure it out.
Anyone else had this issue and solved it?