What's causing the battery drain on my device?

Apps cannot access process information and battery statistics directly, so this feature cannot be implemented by System Status itself.

However, since iOS 8, there's built-in iOS functionality that gives you some basic battery usage info. You will find it under Settings → Battery in iOS 9, or Settings → General → Usage → Battery Usage in iOS 8. You'll find battery usage sorted by apps for the last 24 hours and 7 days.