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I bought a faulty switch lite from ebay that does not start up.

So i opened it up and noticed that it was waterdamaged, there were some spots that had corrosion on it.

So before cleaning i looked for shorts on M92 and BQ and some other places but i could not find any.

Have you looked for shorts around BQ and M92 after updating the handheld? Have the volume up at max, have you made sure the handheld does not output any sound and this is a display issue only?

So i cleaned the board with IPA and tried to get it to boot, i put the official nintendo charger in and it started to boot right after that.

Try hard-resetting the device. Do you get a blue screen, an orange screen, no display and just the battery logo on top left corner or no display at all?

(..) I also tried a known working battery.

What exactly happens when powering on the handheld with this new battery? Do you get a voltage switch? Are you stuck at .40A? How much Amps does it draw?

I checked for shorts again with my multimeter but could not find any. Even though M92 was not shorted i changed it and it still won't turn on. 

Rohm's M92 chip can be tricky sometimes. I remember there was a vid from Alex where he switched the M92 chip for three times, two of them were with his own chips (from his stock). It worked out for him at the third time. Anyway, do this: flip the board over and measure those caps:

They aren't supposed to indicate a short (long beep); If one of them does that, you might want to replace the M92 chip. Yes, again. Or reflow the one that's already in place. Double-check the orientation can't do any harm, so there's that too.

Alternatively, test the cap next to the M92 chip:

If it long-beeps, this means you have a problem with the power management IC. You don't want that to happen, as it's a 90-pin BGA chip. So... yeah.

Caps can go bad sometimes. So test this one below M92. If the cap highlighted in yellow long-beeps, this means the one in red has gone bad:

* Image cropped poorly. Check this link for full-pic: https://ibb.co/LQP10q9

Have a look at the pic below. If you happen to find this specific cap below the BQ chip to short, remove it and test its PADS. If they short, chances are your cap is just fine, but then you might've got a problem with the 9-pin BGA chip highlighted in yellow:

* image cropped poorly. Check this link for full-pic: https://ibb.co/WfMdmPv

So remove it, solder the cap back onto its spot and test it again for shots. You should have no more shorts after removing the bga chip.

Test every single diode, including the ones around the backlight IC chip. Also, pay some attention to the caps around the audio chip, as those love to go bad after the board's gone through a terrible previous owner.

I hope that helps. Report back if you get something.

@rdlf3pro 

Thank you so much for your reply.

Even though i did not find any shorts on the main board i will try to check every single thing you said. 

If i succeed in getting it to turn on i will report back at you. Can take a while though.