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.

There´s a lot to do when problem is battery not lasting, mostly it´s user´s fault. 5 hints that may double your battery:

• close all unused app - You hit home, but app is still running! use an app to free mem and close them up, or close 1 by 1, in multitasking bar;

• set you brightness lower, and smaller time on autolock - Screen leds are one of the items that uses more bat power. with low brightness, lower power consumption;

• only activate 3g when you´re really using it! The same with WiFi, Bluetooth Etc. Using SBSettings makes it even easier (cydia tweak);

• why location turned on 24/7? let it on only when you want to use it!

• full cycle bat once a month - let it drain almost completely, and charge it for at least 8 hours with all apps closed;

• less notifications, or shut it off - notifications also uses a lot of resources, as run in background most of time.

my iphone4 lasts up to 4 days, so I assure it really makes difference!