Average battery life of iphone 3gs?

What is the average battery life of iphone 3gs

It can vary, if you use the battery to the extent of it completely dying and then charging it, the phone should last around 12hrs. But if you are constantly using Wi-Fi, 3G, Bluetooth or even using full brightness the battery life may be decreased by 50%.So technically the battery life is good with around 6-9hrs of battery life.
Hope this helped!