[T-Mobile Samsung Galaxy S II SGH-T989] tjbiker031:
Well i been noticing a lot of people complaining (or commenting) on bad battery life on a ROM they just flashed. I decided to start a thread on how tips to improve battery life. It's not necessarily a ROM that gives you bad battery life (specially if most people comment on how great it is)....there might be a few thing you or your phone is doing to cause this.

First: After flashing a new ROM, you will have the worst battery life ever. The battery will have go through a few cycles before battery life will be apparent. It is also worth noting that sometimes a battery calibration will have to be done by either traditional methods or by the Die Hard Battery Calibration Script by Zeppelinrox. (Not sure if it really works, never tried it…..but its worth mentioning)

Second: Turn off unnecessary sync’s in the phone (toggle button) and apps, such as Facebook, XDA (sorry xda), emails…etc). Yes it is cool to have your Facebook notify you every 30 minutes about somebody’s activities, but that takes up power. I am not saying turn off everything, but you have to find your sweet spot about what is to be on.

While we are talking about deactivating sync’s or limiting them, let’s talk about widgets for a second. Let’s not forget widgets are in automatic sync, sometimes you can control the frequency, and they will use extra system resources such as WiFi, 4G/3G, GPS, etc and this means extra battery usage.

Third: Turn off all radio's such as 4G/3G,WiFi, and GPS when not in use. It goes without saying that if you are not connected to WiFi, it is going to use up battery searching for connectivity. Also, If you notice that you lost signal completely while at work or in a building for an extended period of time, I suggest turning Airplane Mode on. I use Airplane Mode at work and my battery drops 2-3% in 4 hours. You can also turn off data (4G/3G) when you phone is not in use by simply turning off the data toggle.

Forth: I highly recommend using the apps, GSaM Battery Monitor, Better Battery Stats, and CPU Spy to monitor and verify wake locks and apps stealing power. I also recommend Eugine's app, CPU Sleep. All are available on the market and also free on XDA, but why not pay the 2 bucks and support the dev's.

GSam battery monitor used to be Badass Battery Monitor (because it was bad@ss) but i guess too many people complained so he changed it to GSam, but it still is the best out there with very minimal system drain. What this app does is explain to you what is using battery and how much. You can see what inactive app is using battery. It will also show you wakelocks, and what apps held your device awake and for how long. A lot of useful info to help track down battery drain.

Better Battery Stats is a more in-depth info about wakelocks from kernel wakelocks, partial wakelocks, alarms (scheduled wakelocks for each app) and so much more. This can be intimidating to look at and read at first, but you will learn your way around it quickly and what it is telling you. It does include a database link to most wakelocks to help explain most wakelocks.

CPU Spy is useful to be to help determine what my CPU is doing throughout the day and shows Deep Sleep which is very important when tracking down battery drain. This is, in my opinion, optional. Not necessary to track down the culprit of battery drain, but it helps for me.

CPU Sleep is a wonderful app designed by Eugine that when the phone hits deep sleep...it ensures all but one core is sleeping until you wake the device. Far as i am aware, it only works for TW ROM's....i am sure he is developing for CM and AOKP ROM's, if he hasn't done so already.

Fifth: Screen Brightness. Now I know we have a huge cool screen and you want others to see it, so you jack the brightness up to 100% or on Auto. The fact is we have a HUGE screen that loves to eat up battery power like it’s nobody’s business. Now I know putting it on the auto selection sounds like a way to sound power. And in a way it is, but you have to realize it takes more power cycling through different levels. I suggest lowering it low as possible that you are comfortable with. I use 20% brightness, and I feel that you use less power than auto because it’s a constant brightness now going from dim to bright and everywhere in between. (-thanks mrrobc97 for the reminder)

While we are talking about displays, mrrobc97(thanks again) also brought up the about turning off landscape views, not to use live wallpapers, and the use of dark wallpapers and themes.

He also reminded me about disabling apps on startup .He and I recommend the app Autostarts from the playstore. I highly recommend this app over anything I used, including Rom Toolbox’s feature that does this. Not to downplay Rom Toolbox in anyway (it is a great app) but I have had bad luck lately with the autostart feature in the past…probably my own fault for fudging something up I shouldn’t have been (usually disabling YouTube is when it goes haywire with FC’s). Autostarts is a bit more advanced then RT’s autostart tool.

Sixth: 3rd party app killers do nothing. Yes they kill everything running on your phone, but the apps you just killed in your background will restart, thus using more battery power to start back up than it would of if you just left them running. This also is the same when you do this in the stock app manager too. (thanks blunified for the tip).

If you have anything to add or correct, please feel free to post and I will add.

Right now i get about 17-20hours on average of battery life on a work day, and 20-26 hours average on a non working day.

The best so far I have a screenshot for....18 hours up, used 57% with over 9.5 hours left (average).

Update 7/29:

Revised my original post and added in tips from members mrrobc97 and bluntified.