iPhone battery life is awful even after replacing it
It is a common issue for an iPhone to have premature battery life draining, I can't speak to the self replacement, but generally the fastest and best course of action is to follow the steps for syncing your information to a personal information management software(address book, ical, etc) and restoring the device as new.

The step by step instructions are listed in: 
 How to back up your data and set up as a new device

Again just to reiterate, you do not want to restore from a backup in iTunes, but restore the device into a factory default state. If it isn't fixed by that, it's likely a permanent hardware problem.