iPhone 6 battery suddenly draining fast

My wife also had the same problem on her iPhone 6 two months ago. Same steps, we turned off background apps and shut off bluetooth and so on and so forth. All the troubleshooting steps Apple mentions online. Which by the way don't make sense because the phone went from working perfectly to all the sudden not being able to hold a charge almost overnight. My wife is not a power user either and has very few apps she actually uses. Anyway I took it to the Apple store and waited in line for a couple of hours and at that point insisted that they replace the battery even if I had to pay full price for the repair which was around a hundred bucks. For me I'd rather pay the 100 bucks to make the problem go away than have to spend half a day standing in line at a crowded Apple store. Anyway, that worked and she hasn't had a problem since.

Also a new map feature showed up recently, or I just started noticing it, 'Show parked location' where the phone is now periodically popping up a notification saying it saved the location of my car. My opinion, there must be some power consuming process running in the background that monitors my phone and decides that I have been in my car and parked it so it can save my location and show me a notification. I turned that off using the switch in the 'Maps' settings window. Will see if that makes a difference. Has anyone else noticed this feature? Is it new or I just didn't notice it before?