The iBetterCharge is a Mac app that notifies you when your battery on your iPhone is low. Sure you can check your phone for low battery life. The iBetterCharge offers a better solution that monitors your battery 24/7.
The iBetterCharge app communicates with your device via iTunes Sync. iBetterCharge does not install anything to your device so it does not reduce battery life.
Check out the Mac app HERE