[Upgrading, Modifying and Unlocking] TechX1991:
I've always been a lover of Android in the regards of how customizable it is. I've released a few custom roms in my time, mostly for the Galaxy S5 since the battery life on it was kind of honestly terrible when it came out. My roms were all based on Android 4.4.2 as 5.0 just seemed to kill a lot of my battery saving techniques. I figured I'd make a small post about my favorite ways to save on battery.

By the way, sorry if this is an incorrect section. Feel free to move it if needed. Been awhile since I've been on here...

Simple Methods

These methods don't take any special 3rd party app installs or file tweaks. These are simple adjustments you can make in your Settings application right on your device!

If you aren't using your GPS/Bluetooth/Wifi, Turn it off!

A lot of people just leave these things running constantly even when they aren't needed. I look at my fathers S3 and always cry a little inside because EVERYTHING is turned on. The reason its bad to leave these on even when not being used is because Wifi and GPS scan for a connection/location every 180 seconds (depending on phone model). This KILLS battery life so much. It takes a lot to power that little gps, and honestly even more to power that scan for Wifi to connect to. If you're feeling gutsy, you can even turn off your Data connection, but you'll still get text messages and such. Just can't browse facebook.

Haptic Feedback

You know, when you touch your screen and it vibrates. Doesn't seem like much but think about how much you use your phone. How many text messages are you typing? Facebook posts? Twitter posts? Your phone is basically constantly vibrating as you tap tap tap away at that little virtual on screen keyboard. Can we go back to hardware keyboards please?

Screen Wallpaper

This is a biggy, especially on high end phones. That HD screen takes a lot of power, but most of these screens on our phones like the Nexus, Galaxy, and high end LG's all have high end AMOLED screens. These screens work in a really cool way honestly. The darker the color on your screen being displayed, the less power the screen needs to actually show that color. White takes the most power, so if you have a brightly colored wallpaper and are wondering why your phone is dying quickly, this is definitely contributing. I always personally use a textured black background. 100% black (#000000 for you nerds out there) uses literally no power to display. The pixels actually turn off to display that color. The more 100% black in your background, the less battery power you use to display that background.

Screen Timeout Timer

Not using your phone? Turn off the screen. That easy. My timer is set to 30 seconds. I don't have a pass code on my phone because frankly, I don't care if someone gets into it. There's nothing weird on my phone that I know of. This is just one of those simple things that generally slip the mind of some people.

Fancy Features

Do you really need Multi-Window or that fancy Toolbox setting turned on? Just use your multi-tasking and switch back and forth. I use multi-window rarely. It feels like a gimmick to me personally.

Themes and Design

This harbors back to what I said about the whole "the darker the better" above with wallpapers. Using Material Design on your Android 4.4 or 5.0 will save on life because the colors are darker over all for almost everything. Anything white is going to use more power... Sound familiar? Alright, racist jokes aside, this is the truth. More power to display brighter colors. If you have the option, change the theme. A lot of apps have a built in theme changer. Things like Custom Launchers, GO SMS, Textra and many more have the customize ability to set those bright colors at bay.

Multi-Tasking, can you live without it?

This is a BIG saver on your battery, but also one you might realize you really might want to skip. I do a lot with my multi-tasking. Switching from Mobile Chrome to Text messages to a game I'm playing, this can take its toll. Turning off Multi-Tasking entirely isn't exactly the easiest to do either. You need to enable your Developer Settings on your device. If you're curious, go into your Settings App, open About Phone/Device, and tap repeatedly on Build Number. This should unlock Developer Settings. Once in there, you can scroll through and you'll find something with a name like "Limit Background Processes." If you tap on that, you'll be able to control just how many background apps can be running at a time before it starts auto-closing apps. I believe standard limit is fairly high, so setting it to 2 or 3 should help on battery usage.

Installed Apps

This is a big one. There's a lot of apps out there that when using them, or even NOT using them, they eat your battery, RAM, and processing power, alive. They just kill it. The Facebook's apps, Messenger and Facebook itself, were rated in the Top 5 for worst battery hogging apps of 2012, 2013, 2014 AND 2015. Delete those 2 apps and simply use your web browser to login to your facebook. Also, Mobile Chrome is a huge battery hog. Switching web browsers can help a lot. You can see which apps are using the most battery in your Settings by looking at the "Battery" section in your Settings app. Also, don't fall for the "Battery Saver" apps. They use more battery than they're worth and often just "emulate" some of the things I listed here that you can do yourself.

That's really about it for what you can do on a non-rooted devices without 3rd party apps. In the next section, I'll go over a lot more options with Root options and 3rd party apps.

Rooted options and 3rd Party Apps

This is the section that you'll want a little experience with. Backing up your phone entirely before continuing may be a smart option. Check XDA for the easiest way to back up your device before continuing.

Are you rooted? Kill that Bloatware!

A HUGE plus in Rooting is the fact you can remove a lot of the crap-ware that companies like Samsung, Verizon, AT&T, LG and many more of the cell phone companies out there install on your device. Not sure what you can delete? Look for things with something like "Samsung" in its app name. Or, you can go on the Play Store and grab an app called Root App Deleter. This is what I use. It has a nice Junior mode, for those who are new to this, and a Pro mode, for those experienced users. This will help you identify what you can and can't delete.

Type of root You have

There's always some sort of exploit to get root opportunity on a device, but what a lot of people don't know is that most of the Root exploits out there are called "live root" exploits. What is a "Live Root?" Well, that means the process of needing root is constantly being ran and controlled in the background while you may not even realize it. Running a Live Root will usually make your device run hot and slower. A big complaint of a lot of Rooters. Within the last few years, root exploits have gotten better, and there aren't as many Live Root exploits left, but for some devices, its the only way. To know if you have a Live Root, simply check your settings and see if your Android System is using a lot of battery power. That'll tell you. The best and I'm pretty sure only non-Live Root exploit out at the moment is KingRoot and TowelRoot. TowelRoot I trust more than KingRoot because KingRoot was made to attempt to work with ALL devices, where as TowelRoot was mainly focused on 1 specific Kernel version and Android version. Thank you GeoHot for TowelRoot. What a LIVE Saver.... get it? ... I'll see myself out.

Custom Roms

A lot of Custom Rom dev's out there focus on MORE instead of less, and those are the roms I usually steer clear of. These "more" options use a lot of battery power, even though they usually claim it uses less. The best Roms to install, in my opinion, are the ones that don't have many "new" features applied. Build.prop edits are alright, things like init.d support don't hurt anything, that usually helps honestly. The simple Debloated Dex'd Base roms are the best. You can always customize it later. A great example of a good base rom that gets good battery life is one I released a long time ago when the S5 was released. I'll leave the link below to XDA. The project is dead, but I may revive it

XDA BoxxiRoms v2.0.2

I'm in no way bashing custom rom development. New features are always awesome to have. They're cool, they bring new life to an old device.

PixelBatterySaver...

This is the ONLY app I trust to SAVE battery life because I've proven myself how well it works. While I said above that Apps don't work and use "more power than they're worth," this is the exception. This app, when activated, leaves a black mesh over your screen. and turns off pixels, but its enough that you won't notice during regular use. There's also multiple levels you can use. If you're interested in this, check it out on the play store and give it a go

Pixel Battery Saver Playstore

This is just the tip of the Iceburg for what I know honestly. I'll post more soon.