I've had an iPhone 7 since launch and as of the past month, I noticed a strange battery drain problem. Sometimes, the usage and the standby times are exactly the same, meaning that my phone is being used by an app in the background without me knowing or something. This is always solved by restarting the phone but it occurs again after some days randomly (could be a week or less before it happens again). At first I thought it was a bug of iOS 10.1 but after updating to 10.2.1, it has happened again twice. After some research online, I've found several other people having similar problems dating back to even iOS 8, so I'm stumped. Has anyone here ever had this issue? Is it a bug or hardware fault?