iPhone battery can last hours longer with this new iOS9 feature

Keeping Low Battery Mode on all the time could take your battery life from 12 hours to 17 hours

Low Power Mode has been one of iOS9's better-received features (Pablo Blazquez Dominguez/Getty Images)

Amongst iOS9's new features (some of which have been received better than others), Low Power Mode is one of the most useful.

You've probably already seen the notification if you've upgraded - once your phone's battery drops below 20 per cent, Low Power Mode turns on, cutting down on background app refreshing and visual effects to make sure you get the most out of your remaining juice.

Once you charge your phone above 80 per cent, Low Power Mode switches off, and you get the full functionality of your iPhone back.

However, if you want to get the most out of your battery all the time, there are ways to manually switch Low Power Mode on even when your iPhone's fully charged - potentially extending the amount of time you get on a single charge by hours.

One of the easiest ways is just to ask Siri to turn it on for you. Alternatively, swiping left on the home screen notification when the mode has been turned off brings up a button that allows you to switch it on again.

Going to Settings>Battery>Low Power Mode will also let you switch the battery-saving feature on and off as you please.

Apple haven't said how much extra life you get out of your phone in Low Power Mode, but in an in-depth test by Wired magazine, they found that the battery lasted 1.43 times as long with the mode switched on.

So, if your phone usually lasts 12 hours on regular mode, keeping it in low power mode could extend that to somewhere in the region of 17 hours.

Obviously battery life depends on how much you're using your phone, but having a few hours of extra power is always going to be handy.