Low Power Mode is one of the new features of iOS 9 that allows you to keep your battery usage as low as possible throughout the day when you want to conserve battery life and you feel your battery level is getting to the point where you might not last until you can get to a charger.
Unfortunately, while most of us enjoy reaping the benefits of Low Power Mode, whether we have a low battery level or not, iOS automatically disables the feature when your device gets charged up enough, forcing you to go to the Settings app and re-enable Low Power Mode manually.
That's where a new free jailbreak tweak in Cydia's BigBoss repository called LowPowerMode is going to make your life a whole lot easier.