20 - 30 minutos
The battery on my nearly 3 1/2 year old phone was only lasting about a day with just moderate usage.
The process went very smoothly with the exception of removing the ribbon cable, labeled 3. The plastic flip up locking mechanism is very delicate as are the two pieces on either side of the cable. I managed to damage them and had to jury rig a replacement to lock the cable in. All in all it took me about 25 minutes from start to finish
I would suggest having some electricians tape on hand in case you do damage the locking mechanism in step three. While not a perfect solution it will do the job nicely.