[T-Mobile LG G2x] spencersir2:
Ok I have been reading since literally the first day the G2x came out about the "Horrible" battery life of the phone. So, after toying with it for about 8 days I have nailed it down so that the phone gets about 20 hours of Moderate use(Constant texting, internet for emails, YouTube, and searches, and probably about 2 hours of light gaming(not Nova or NFS)). So, Outside of the obvious like make sure your bluetooth, wifi, and GPS are off and turn your display brightness down here are my steps to Better Battery Life.

First - Root The Phone. There is plenty of links and help if you don't know how or have questions about rooting.

Second -(Root Needed) Use Titanium Backup or Antek App Manager(Antek is free) and Freeze or uninstall all the bloatware that you don't use off of your phone. Especially Car Home cause along with people on XDA i have also noticed that it does use a fair amount of battery for NO Reason.(Be careful with My T-mobile and My Device might throw your phone into a force close frenzy)

--For some reason people have been asking exactly what T-Mobile Apps you can freeze/uninstall and the answer is. All of Them. I personally left My T-Mobile(To view Minute Usage) and Wifi Calling(Cause I have no service in some buildings) and froze the rest, but you can get rid of everything you don't want or use.

Third -(Root Needed) Set CPU. Have had this on my G1 and N1 and it does nothing but save battery. I currently have it set on 216 - 1000 for when the screen is on and the only profile i have is for when the screen is off and it is at 216-216.

(Alternative) Pimp My CPU. I now am using this for my G2x because I am running custom kernal. Personally I like Set CPU better, but do to the fact that Set CPU can't get past 1000 MHz makes it kinda useless for the G2x Tegra 2.

Fourth -(Root Needed) Battery Calibration. There is an App in the Market for this and it is easier and less of a hassle than Factory Reseting the phone. Just charge all the way to 100% and i discharged to 0% and recharged it and Amazing difference in battery life. (And don't doubt the Calibrator cause right after i set it to calibrate the initial 100% got to zero in about 7 hours, but after that one cycle i was getting the 20 hours i am now)

Fifth - Elixir. Not only does this app display anything you might wanna see about your phone (CPU usage, battery temp, battery percentage, memory...) it also has a widget that lets you toggle your internet on/off. Which is almost necessary since "4G" kills battery like no other.

Sixth - Auto Sync. I shouldn't have to put this, but if you don't know your phone is set up to auto sync all your Google apps(Calendar, Gmail, Contacts) and Social Network apps(Facebook,Twitter). So go into settings and make sure that you turn auto sync off.

Now the next steps aren't proven to give extra life, but i did them just in case and well I get 20 hours of use like i said before.

Sixth - Watchdog. This app monitors all the other apps and processes in your phone and will alert you if a rogue app is draining your better life.

Seventh - I did the "Alternate Battery Fix". This involves changing one setting and who knows maybe it does help me get extra juice.

Link: http://xdaforums.com/showthread.php?t=1051036

Eighth - Wifi Never sleep. Supposedly according to some if you change wifi to Never Sleep it will stop some loop in the programing which in turn will save battery.

Ninth - Wifi Calling. If you didn't decide to freeze/uninstall this app. Make sure that this is OFF, because whenever you have wifi on it will constantly flip between Wifi Calling and normal radio towers, which once again is bad for your battery life.

Well, Thats that and if y'all can think of anything that i missed or have any questions or ideas let me know! And remember this is a Dual-Core, High-End, Monster Phone and duh if you use it hardcore (Movies, HD Games, tons of web browsing) the battery will die fairly quick.

P.S. Will post a Screen Shot of Uptime for 20 hours later(if it doesn't Re-boot before i get to 20)

Update #1: Have read all the posts and have decided to speak up about a couple things.

Task Killers - I feel like these are brought up in every thread ever created about batteries, and well they are useless. So, if you are gonna bring up the ram usage argument. Android is made to kill programs that are either inactive for to long or the operating system will shut down background tasks if a new app needs the cpu power. Than for those who say that it helps close programs and makes the battery last longer.Having a Task Killer that basically re-closes the same apps over and over again(These are usually bloatware background apps that for some reason never stop running) is not gonna do anything except waste precious battery life on running the task killer itself cause the app will just restart. Your best bet is to run watchdog find the apps that are taking to much battery and freeze/uninstall them.

Managing Apps - Apps like Tasker, Juice Defender, and the like are in my opinion not battery savers at all. They are just tools to implement what i have already previously stated, but that doesn't mean that they aren't useful. They are good if you have a busy schedule and have to constantly turn the internet on and off or switch between certain settings, but they are not actually a cause of better battery just a tool to implement what you could do on your own.