[Xperia SP Q&A, Help & Troubleshooting] tyrael_pl:
Tested and here are the details

First off i want to state that i am grateful to everyone and anyone who contributed to finding this solution. At no point of the following comment i am trying to be rude of ungrateful, i will only try to share what i managed to notice to give a fuller feedback.:angel:

I successfully replaced the apk file as instructed :victory: however the following are the changes/glitches i noticed, compared to way STAMINA worked on the previous soft (iirc 1.257):

[change]If both STAMINA mode and Low batter mode are active at the same time they have a shared icon - 2 smaller icons, each of the respective mode, on one field. In practice it is just a space saver since both modes need only one icon space. Before this change when both were active each had one big separate icon. If one of the mode is active it has its large icon like it used to.

[bug]The bar blinking effect for unread text msgs (sms) sometimes stops working, effectively giving the same effect from before this change. I noticed it happened for example after i talked over the phone. Only a phone reset restores the desired and aimed functionality - unread sms led blinking in stamina mode.

[bug]The custom light effect for separate contacts' for unread sms does not work properly (global works fine but needs reset after a change). Example: i set Mr. X's light effect in the phonebook to green. The global effect for unread sms is red. Led blinks in red in stamina mode while it should be always green, however blinks for a split second green upon receiving an sms. Calling is still green while global setting is set to other color.

[bug]Shortly after the change my phone had very low gsm reception 0-2 bars while it has always had full (4) in the place of my test. I live in the center of one of the biggest towns in my county. Turning stamina on and off and reseting the phone restored my full gsm reception permanently - 4 bars.

I have my doubts about the "new stamina's" battery saving efficiency but I have not confirmed that... yet. If i manage to conclude anything of use I'll let you all know.

:highfive: Once again, thank you for this solution as it restored the near previous state of things i was desperately looking for. One last thing, if anyone would like to, here is a sony link to the problem. Peace.

Update edit 30.09:

I am afraid i dont have good news for anyone interested in this solution. Here is what managed to measure and see. While phone is on standby everything seem moreless alright i used up 3% of batter in 6h which give a ratio of 1%/2h which is fairly standard from what ive read. The fun begins when you actually use the phone... and i dont mean heavy usage like games, i mean looking thru options or apps. Really things like browsing your phone with wifi and gps on with screen set to 15% brightness. God... my battery seem to be drained hard, i see -1% every few minutes which i dont recall to happen. The most extreme case i noticed was once after a reset and after about (maybe) 10minutes i went from 100% to 95%.

In the best possible case scenario with screen turned on all the time for the test it took me 6 minutes to use 1% in a near idle state: running stopwatch on static screen with no scrolling etc, and not many processes in the background. Which means that i would drain my battery whole in 10 hours of doing nothing with the screen on 15% brightness. Likely browsing would drain battery even faster. I clearly recall having much better performance with the stock stamina... sadly. I will revert, do the same stopwatch test and report back.

Edit: It took me 7 minutes to drain 1% of battery in the same stopwatch test while using stock stamina with bugged sms led function and i guess ill have to stick with that.

I dont want to suggest anyone not to use this fix but maybe do some tests of your own, perhaps its a placebo effect for me. I would gladly see what are the tests and impressions of other people. Thanks again for this fix :) Peace.