iPhone 6/6S Battery Case

The iPhone 6/6S Battery Case is a great idea.  I was excited to receive and use the battery case.  After charging the case for the night, I put my iphone in it and headed to work.  After a few hours I checked the battery case to see how it was doing.  My phone and the battery case was off.   I turned the case and my phone back on and went about my day.  I checked about 30 minutes later and they were both off again!  I took my phone out of the case and made sure that I had put everything together the correct way.  I found out if I slid my phone halfway in and then turned the case on it would stay on for about fifteen minutes.  Otherwise it would shut both off after about five minutes.  I am hoping that I have a defective case and that another case will yield different results.  As I said it is a great idea, just need to work out some bugs.