iPhone 6 Plus battery reduced to a fourth of what it was recently
iOS 9 lets you see exactly what's using battery over the past day and the past week.


Go to Settings > Battery
Wait for the list to populate
Tap "Show detailed usage" to see a breakdown of foreground and background usage for each process
Switch between "Last 24 Hours" and "Last 7 Days" to see what might have changed for you 2 days ago.


For much more on this feature, including some advice on how to make sense of the data, see http://www.imore.com/how-see-whats-using-battery-life-your-iphone-or-ipad