20 - 30 minutos
My battery was kaput and Apple offered to fix it for $80. I did some research and found I could give it a shot for ~$20. I figured if it didn't go well I'd just upgrade which was what I thought I was going to have to do before I found out that the problem was the battery. The symptoms:
1) battery draining ridiculously fast
2) phone shutting itself down with battery life at anywhere from 65% or lower (no warning) - phone could not be restarted without a hard reboot and sometimes not without being plugged into charger.
Repair was relatively easy - managed to follow instructions and swap out battery. Hardest part was taking off the glass since I neglected to order the suction cup and thought that since I had ordered the kit I would have all the necessary tools. The new battery is better but definitely not as good as the phone was when new. Battery still drains in 1 day and much sooner if I'm actually actively using it. It will also shut down w/out warning but only when the battery is < 30% and now when it shuts off it's done, not to be restarted w/out the charger. I can probably postpone an upgrade for a few more months - this is basically a bandaid and bleeding is now manageable.
Follow directions and you should be ok. Think about ordering the suction cup - it will probably save you some frustration.