[Galaxy S 4 i9505 Android Development] davtse:
Okay, I did a post like this for the S3, but the thread's been closed so I'll repost this here. Hopefully [MENTION=4401403]friedrich420[/MENTION] doesn't mind.

A consolidation of battery tips that I've come across during my time on the s2, s3 and now updated for the s4.

For use as a reference,

Previous post, credit droidphile

This is the breakdown of power draw of the various components in the s2. I don't have the details for the s4, but we can still take references from the little brother.

Battery saving tip 1: Turn down your screen brightness and use a dark theme!

Our S4 use an amoled, and less lit pixels it uses, the more battery you save. The amoled system utilizes individually self-powered/lit pixels, which means black pixels are unlit, and this is why the darker the background, the more battery/power you save. black backgrounds and wallpapers are potentially the best battery savers of all.

Turn down your screen brightness even further using apps like Lux autobrightness. I find the lowest brightness setting in TW too bright for dark conditions(0 lux). Lux allows me to dim it so I can read comfortably in the dark.

Battery saving tip 2:Use a modem that suits your area best!

This tip requires patience and experimentation. A modem that comes with your original firmware might not be optimal for the network in your area. I found this out the hard way. The difference between an optimized modem and an unoptimized one is noticeable. I went from a full 1% per hour idle drain on my extended battery to an average of 0.2-0.4%. It takes some time to find the right modem but the end result is certainly rewarding. An optimised modem will not keep switching from 2G ->3G ->H+ -> H etc, and as you can see from the above, ALOT of power is used when switching bands. If you want EVEN more battery savings, you can use the intelli3g xposed module to control your network, changing to 2G when your screen is off and inactive. I've had nights where with data on, push subscriptions on for gmail, facebook,facebook messenger, 2 whatsapp accounts(WA +OGWA) and had 0% drop overnight. There will however be a drop in connection as your phone changes from 3G to 2G. Do not use if you can't tolerate the short interval of dropped connection.

Battery saving tip 3: Optimize your usage, turn off whatever you don't use!/deal with your wakelocks

Don't use bluetooth/wifi/GPS/NFC/sound(volume)? Turn them off, or at least lower their polling frequency(possible with wifi, not sure about the rest)

Don't need an app running in the background? Use greenify to hibernate the app. The more deepsleep your android device has, the more battery you will save. Some apps are especially nasty and run in the background even if not required to. Use BBS(betterbatterystats) to find these rouge apps and wakelocks that are keeping your device awake. Some wakelocks can be dealt with using xposed module "per app hacking" that prevents it from applying a wakelock when not in use. wakelock terminator also works well but is a paid application. I personally combine greenify with tasker to hibernate apps whenever the screen has been turned off for more than 5 seconds.

Battery tip 4: Samsung powersave mode

Samsung powersave allows you to limit your CPU freq and lower your screen brightness further. This allows you to save juice and as we all know, ever little bit counts! Lower freq will need less juice as compared to higher freqs and generates less heat. OC steps require the most power and are IMHO quite pointless because the s4 already has a beefy processor.

Battery Tip 5: Samsung ultra powersave mode

We don't have working ultra powersave mode for the s4 yet, but we can emulate this by combining the use of the intelli3g xposed module with tip 4 AND the use of chainfire's CF lumen. The ultra powersave mode basically turns off your data connection when your screen is off, and terminates unnecessary apps from running in the background. CF lumen turns your phone completely greyscale, which helps because of the amoled. Using intelli3g we can still have an active data connection while extending battery life substantially.

After you have done the above, you can try

Battery tip 6: Undervolting

Undervolting can save some battery, but I feel that compared to the above tips, the amount saved is not as significant, although it is still noticeable. It also reduces the heat produced by your device.

Take note also that by undervolting you will increase the risk of instability/freezes/reboots and data loss. Do this only as a last resort, and if you know what you are doing.