mobile

As the title sugests one of the main goals for everyone who scrolls and uses his OPO either to avoid awkward situations, for work or simply to check social networks etc, you want to have the best GOD DAMN Battery life you can possibly squeeze from your 3.1k mAh battery !

I am not responsible for any damage to your phone. Read before downloading or posting in the thread. Proceed with caution if you have no experience.

So to start off, i'm already assuming you have your OPO rooted, which is a must for this guide.
So you can go for any custom ROM of your choosing as long as it supports the Kernel of your choosing.
Before trying to say which Kernel is best, i'd like to state that I have a really simple philosophy which is,If it ain't broke don't fix it, so I go with the AK Kernel because it never failed me, has a really good comunity to back it up and is the only tested kernel for the OPO in the UKM Thread.
( Don't worry i'll paste the links to all of these things that I'm speaking of ;) )

After you got your Kernel up and going you're gonna download the UKM ( Universal Kernel Manager ), which will enable you to use Synapse on your device.

So now you have the Kernel and UKM, which means it's time to flash them all.
Now flash your UKM file and after installing it flash the Kernel and you should be set!

Once the Phone has booted, just make sure to download Synapse from the playstore. I wouldn't recommend changing the voltajes on your cpu because you can really **** your **** up which no one wants!
I'm running with this profile for over 3 months and it has done me wonders ( pics below )
Synapse Screenshots

This means your CPU will be running 1.3 GHz less about 80% of the time, the suspended Cpu frequency will be 300-400 MHz lower and the GPU which goes to an all time high of 578 MHz every time you install a new custom rom will be lowered to 200 MHz. This will result in about 40% more battery AT LEAST.
I don't have any photos showing my battery time because i'm a bit stupid, but the next week i'll try to screenshot my battery life and show you, however, I do know that i'm averaging about 6 hours SoT with both Wi-Fi and Data turned on 24/7.

Also a really good and must have App that goes really well with this is Leandroid which makes your Data shut off after X minutes of the device being disabled. If you feel you're device is running low on battery because of uknown sources, I advise you to download Wakelock Detector to check if there is something keeping your cpu ramping up when it shouldn't be.
This is not optimal for a 3.1k mAh battery but, keep in mind that the memory leak issue is still in the works and this is the best I could do in the given situation.

Another point I would like to focus before ending this post is the screen brightness. We all know that Android L stock Brightness control sucks ( if you don't now you do :P ), so I recomend using Lux Lite, which controls your screen brightness by adjusting it whenever it receives more or less light in the sensor, and it has worked wonders for me, it you're interested in a profile I will link mine

Now I won't bore more, I hope this "guide" was helpful to you and if you liked it don't be shy to press the thanks button.

Links
Kernel
UKM
Synapse
LeanDroid
Wakelock Detector
Lux lite