Starting with iOS 7, Storm Shield uses the Background App Refresh feature in conjunction with Significant-Change Location service (a combination of GPS, cellular service and WiFi) of iOS Location Services in order to notify you of weather alerts for your current location (for more information on Apple Location Services, click here). This provides a low-power way for apps to get a device's current location without using GPS and still be notified when significant changes occur. This has a minimal effect on battery life. Battery life depends on a variety of factors such as the version of iOS your device uses, the age of your device and its battery, and other apps using your location.
If you turn off your iOS Background App Refresh, Storm Shield may not be notified of changes to your current location as often as is needed to send you weather alerts for your current location.