Now there's a way to find out - but it might make for surprising reading.

A new feature in iOS 9 tells iPhone users how much time they have spent browsing the internet and using different apps such as Candy Crush, for example. 

To find this information, iPhone users with the latest software can go to the 'Settings' menu then select 'Battery', before tapping the clock icon at the top right of the list of apps.

They can then see a breakdown of their activity in the past eight or 24 hours, for example, with the apps they have spent the most time on at the top of a list, and the least popular at the bottom.

For each app users can see how much time they spent interacting with it and how much time it spent running in the background.

For example, MailOnline found one user spent 10 minutes looking at Facebook, while the app spent 47 minutes running in the background. 

It's immediately noticeable that low mobile coverage drains battery too, with 'No Mobile Coverage' accounting for one per cent of a user's battery.

iOS 9 also sees the introduction of 'Low Power Mode,' a feature that Apple mentioned at its worldwide developer's conference in June.

The feature is similarly found in the Battery menu in Settings. 

When a phone's battery slumps below 20 per cent, iOS will ask a user whether they would like to switch it on.

It stop apps and emails refreshing as well as automatic downloads, for example, to help a handset last longer.

It is automatically disabled once it's plugged in again.

Apple claims that power efficiency improvements will give some users an extra hour of additional time before charging.

These battery improvements should be seen on all devices but will more significant on newer devices with hardware that is powerful enough to take advantage of them.

iOS 9 also offers dynamic wallpapers, a smart news app and a cleverer keyboard. 

Apple has also added an app that makes it easier for Android users to switch to iOS. 

Called 'Move to iOS', the app securely transfers contacts, message history, camera photos and videos, web bookmarks, mail accounts, calendars, wallpaper, and DRM-free songs and books. Elsewhere, the Move to iOS app will help users rebuild their app library. 

Any free apps, such as Facebook and Twitter that have been installed on the Android device will be suggested for download from the Apple App Store. 

It's available to download for iPhone 4s or newer, iPad 2 or newer, the iPad mini and later models as well as the fifth-generation iPod touch. 

On the iPad, new multitasking features have been added so users can split the screen between two apps for the first time, or use them both at once. 

Apple said these new features will enable iPad users to 'make even better use of its large screen'.

(dailymail.co.uk)