Sudden power off solved with new battery !!!
Finally tested it today and it really works!. The real fact is on web you always find that "it should" be the battery, and a battery change "whould" solve it, well I have to try it and it really does, so you should get a battery somewhere ( check out I found 2 places on www, dunno if I can put the links please say If I can do so ) and get your phone alive again! ( I'm so happy
Here are 2 dissasemble videos; one from our friend "danieldp1990" and one in russian HD. Whould reccomend use both of them since as nice as the russian video looks, they're missing some parts.
The most hard part is to remove the battery since it's glued and you don't wanna do much strenght since you have the display right below it, so make it slowly.
Best of luck for the ones that have no warranty left!
PS: I think we can stop looking for soft / alternative solutions.