[Xperia Z3 Android Development] Tux111:
Sure, let me help you. I'm specialized to write newbie guides xd.

I suggest you to use my method, that i used more (probably) then 10 times right now (there are probably faster ways, but i like this).

1 -

Flash Stock Sony ROM 4.4 with flashtool

(called Sony Mobile flashed by Androxide, i use 0.9.23.2 version), clicking on flash icon, selecting "flashmode" and setting APPS_LOG and USERDATA under the section WIPE (to assure, when 4.4 rom will boot up, no apps start to crash all the time and make phone always reboot). To flash, simply start the process, shutdown phone, Volume Down and connect phone to PC. Flash will aut. start;

2 - After 4.4 ROM boot up,

ROOT it with giefroot 3.1

. To do this, you need to enable USB debug, mock locations and remain active options in Deleoper Options. Also, for giefroot, you need to set Flight Mode and to shut down GPS, NFC and Bluetooth if theyre active. After this, you can easily ROOT;

3 - At this point, if you want,

you can make a backup of DRM keys to save sony algorithms

. Do it with Backup-TA-9.11 tool that you can easily find on web. Really easy, just connect phone and follow terminal infos;

4 - At this point, you

MUST unlock your bootloader

. For doing this, follow this link, select Z3, and follow site steps (it will ask for IMEI and e-mail. Check spam folder.). After e-email arrived, follow the link inside e-mail and you will simply have to follow sony bootloader unlock steps. Quite easy, you need adb, a cable, a terminal and write down inside terminal sony guide commands. Be sure you unlocked your bootloader before proceed.

5 -

Root again!

Bootloader unlock will remove root and reset ROM, but previously root was obligatory to make a correct TA-partition backup.

6 -

Time to install Recovery

. I used NUT Dual Recovery (avoid XZDualRecovery-2.8-RELEASE, it will not work, idk why). Another easy step: just connect phone, accept root and let him flash recovery;

7 - After this recovery install, you will directly be inside recovery. DoWipe Data, Wipe Dalvick Cache and Wipe Cache and install ROM. Immediately after ROM, install Google Apps 7.1. Immediately after Google Apps, install SuperSu 2.82. After all this, you can finally reboot (don't let twrp install others things automatically)

8 - Now, ROM will reboot some times. At first start, it will probably stay like 5 minutes stopped. When you see screen brightness goes down while loading boot animation, wait 3 min and shut down phone pressing

Volume Up

and

Power button

. 3 Vibrations and it will shut down. At this point, just switch on the phone and it should start in 2 minutes or less with no prob.

Why using this method?

It works everytime like a charm on Sony Z3 6603.

Why avoid this method?

NUT Dual recovery quite always break down when you install a new ROM that not include a Recovery (not RR case fortunally, that have TWRP integrated). This mean that if you want to switch another ROM, you cant come inside recovery and change it, but you need to repeat the full process up here (reflash stock sony 4.4 ROM ecc.).

---------- Post added at 04:03 PM ---------- Previous post was at 03:58 PM ----------

I already tryed that app some days ago to found the problem, but i unistalled thought it was not working lol. Now i'm going to try again (after reading i need 1-2 hours at least to gain some wakelock informations). Let's see. This battery drain is common in all Nougat ROM for Z3 btw.