iPhone 3G battery wouldn't last one day.
Generally as expected. The guide and video were very helpful. The little plug/snap connectors were easy. The ribbon connector was more of a challenge for me. Battery was harder that expected to dislodge from the case.
I was interrupted twice, once for a phone call and once for someone at the front door. The process would have been easier if done continuously. Watch the install video and review the the guide several times before starting. I followed the guide displayed on my laptop during the install. The first charge of the new battery lasted 3 days.
iPhone 3G Replacement Battery
Phillips #00 Screwdriver
SIM Card Eject Tool