iPhone battery life is awful even after replacing it I have an iPhone 3gs 32gb. As they do, my battery was noticeably depleting as well as conflicted with the device having been slightly water damaged (dropped in quickly but immediately turned off and dried out. Works "fine"). I decided to replace the internal battery with a factory OEM version but even after doing so my battery life is awful. I am talking about losing 10% during one 4 minute phone call or 30% in the first hour or less or simple standby. 

Are there things I should look for or perhaps additional parts which could be causing the depletion? 

For reference: I charged the phone to 100%, turned the phone off, then 3 days later (with phone off) the battery was completely dead. Something else seems to be constantly running or draining the battery.
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.