20 - 30 minutos
The battery was draining fastly and the device was shutting off randomly at any percentage of battery left ,I guess it was due to the high current demand of some applications from my old misused iphone battery.
Although it took 35-40 min to replace the battery since it was my first time ,everything went smooth having the battery replacement guide and following the procedure in it.
The difficult part is the removal of the old battery from the casing . Since the green opening tool supplied the with the battery replacement package is very weak I broke it when lifting the battery with it , in fact it is supposed to be used to lift the connectors on the logic board .So it would be a good idea to supply a L shaped rigid but thin metal lever with package content to lift the old battery at a very low cost-up .