Low Battery Mode might be my favorite thing about iOS 9. It radically improves battery life on an iPhone when your device dips down to 20%.
The only problem? Once your iPhone charges a sufficient amount, Low Battery Mode automatically switches off. Which is a shame, because if you kept Low Battery Mode on all the time, you could eke out hours more battery life from iOS.
Sadly, iOS 9 doesn’t let you keep Low Battery Mode on all the time. But if you’ve got a jailbroken device? That functionality is just an install away.