It seems that the battery usage is much high after upgrading to iOS 10. during day time its not much noticed as the phone will get connected to the USB cable but while in night it gets 70% to zero in eight hours though no apps running.
Check the battery usage in settings to see what is using the battery.
TRy switching off ( Bluetooth ) and switch off auto app background refreshing. Both drain the battery.
Another trick is to switch the AIrplane to ON at night . This will save Battery power .
I've not noticed any changes in my battery life. Also, you might want to take the time to charge the device overnight, that way you have a full charge when you start the day, rather than letting it drain down overnight.
Next, take the time to look at Settings>Battery and find out what app is using the highest percentage of your battery use. You may need to troubleshoot that, or see if there is a process that is possibly stuck trying to run. That can cause battery life issues. Once that is figured out and corrected, you should not have issues.
iPhone 6S Battery usage after iOS 10 upgrade
