How to Calculate that how much time you may continuously use Your Smartphone After full charge

How long does a 3000mah Smartphone battery last?

It depends on the amount of current you drain from it. Lets say we drain 0.5 Amps continuously. Our battery capacity is 3 Amps, so it should roughly last for around 6 hours.
ScreenShots show Discharge Value that 996.799 mA means 0.996799 Amps. Equals to 1 Amps (Say)
To know How much power Your phone use from the battery.

Discharge Value of the Battery :---

Dial *#*#3646633#*#* or, Go to
                                                      Engineering Mode
                                                        > Hardware Testing
                                                                 > Power
                                                                       > Charge Battery


If, Battery Capacity is 3000 mah then,
                          3000 mah = 3 Amps
Battery Lasting = 3 Amps / 1 Amps = 3 Hours

You can use 3000 mah battery phone for 3 hours only with 1 Amps discharge value .