So what i got here is a Switch with 0.42 A , no shorts, and already Patched System. When i try to start it it it shows the Nintendo Logo and then shuts down completely. No Backlight, no sound. I then have to hold power button for 15 sec to repeat the process. When i plug the ac adapter into it it doesnt show the battery indicator.
What i have tried:
-30 second power hold
-Volume Button and power button hold
-Leave it plugged for one day
-Leave it unplugged and turned off for one day
Sometimes the chips could still be the culprit without actually showing shorts, thus I think his answer is not that bad to try out. Or perhaps the BQ chip near the battery.
Good luck!