[EVO 4G Q&A, Help & Troubleshooting] Unknownforce:
A Few things to note here...

LOCATION:

THIS is probably the BIGGEST factor in battery life... if you are getting less than great reception, your battery WILL drain faster... this is simply because the phone has to work HARDER to keep in touch with the tower. With my old Touch PRO (2) and Diamond, there were several radio versions to use and 9/10 times the Telus radio was the best... but since the EVO is sprint only, we only have the two radio versions that have been released to use... and on top of THAT, roms are designed to work specifically with certain radios... So it's not as easy to swap radio firmwares...

USAGE:

Obviously everyone else uses their phone differently at different times of the day and under different circumstances. With that being said, don't think that just because one person gets good battery life means that you should too... Think about what you're using the device for... how often... the amount of texting, web surfing, video watching, music playing... etc...

APPS:

To put it as basic as possible... The more apps you have the more battery you use... Now this statement is not entirely true, let me explain...

Apps can be developed by anyone... That's obviously one of the benefits of using Android/Google... The inherent problem there is though that not everyone develops them to play nice with other apps. With that in mind, the statement above holds true... Certain apps are loaded at startup... widget apps sometimes are not developed correctly and cause battery drains... yadda yadda... Basically it's up to the developer of the app to design it to work properly with the system and exit properly when told to do so... Not ALL of them do that right.

The case that the statement would be not true is that just because the app is installed, doesn't mean it's running... and thus doesn't use more battery at all. (duh)

Just try to pay attention to what you have installed and think about getting a "task manager" that monitors running tasks and can tell you everything that "pings" the cpu.. and you should be able to get an idea of whats eating your battery.

TEMPERATURE:

Temperature affects battery very much.. the hotter the environment the more the battery drains... This holds true with just about any battery. With that in mind... does your phone sit in your pocket while you are working in a 100 degree shop? probably not a great environment... Battery will drain faster... When you're in the office... take your phone out of your pocket and leave it sit on the desk... better ventilation... less temperature... less drain. Just be mindful of where you have the phone in high heat conditions, try to keep it out in the open as much as possible rather than in your sweaty pocket :)

SYNC:

If you have 5 e-mail accounts, facebook, twitter, flickr, etc etc etc... you're battery life will most definitely suffer. I would cut down to as little as possible... I personally use the google stuff as well as facebook... I used to have all my contacts (that are on faceboook) linked to facebook... The thing about doing that is that it pulls their status and other info on a "regular" basis... So you're battery takes a huge hit here... I stopped linking them... it wasn't worth losing my battery life. Also, turn off live feed in accounts that you don't use regularly and just manually sync them when you use them... Yeah, it's an extra step... but if you're not using them that often... it's not worth the extra battery drain...