Ultra-Power Saving Mode:
This mode allows you to save your battery to maximum. You can used this mode when battery is nearly dead. It will dim your brightness and take your phone to grey mode and you can choose apps that you want to open in grey mode so that battery is consumed at minimum.
Battery Saver: This app can also be used as battery saver. when you start the app it takes away colors dims the brightness and show you a limited number of apps and this thing ultimately saves your battery.