I saved $180 by replacing the battery in my iPhone 3GS.
20 - 30 minutos
My iPhone 3GS would not hold a charge and the screen blinked when touched. The Apple employee with an aggrandizing title wanted nearly $200 to replace it with a refurbished unit of the same vintage.
Once I got the device open, I was able to see a bloated battery. The swelling was so severe the casing on the back had cracked. After replacing the original battery, the screen returned to normal since the pressure was removed. My iPhone 3GS now holds a charge.
I used the suction portion of a GPS windshield mount to pry the glass from the body of the 3GS.