So thats the story : my sons nexus run out of battery, switched off and thats where the problems started, when plugged in (wall charger, usb) nothing happened on the screen, no signs of charging. For 1 week I was trying playing with battery cables, HW buttons combinations, different usb cables and chargers, all forums, advices and nothing. Nexus lost his life when battery came to 0%. But today I tried something different. Nexus battery has 6 wires coming out, most important are 2 reds and 2 blacks, I had spare USB cable which i cut and separated both black and red wires. Every cable have more small wires inside of it, so I've made 2 reds ones and 2 black ones from my usb cable and pushed them into battery slot (be sure to put red to red and black to black). I just wanted to see what will happen when battery will be charged straight from charger. Nothing to loose as Nexus was dead anyway. Then i plugged that usb cable to genuine wall charger, left it for about 10mins and then fitted battery back into nexus. Voila ! Nexus booted straigh away with 6% battery and now is charging like always. Looks like battery needs to be kicked in the ass with some volts to come back to life.
Hi. For all those who are suffering from "sudden death" of their Nexus 7 1st gen. I have found possible solution, well at least it worked on mine