DJI Mavic Mini water damage

[dansity]

Hey,
I got Mavic Mini for basically free. It dipped into a lake but managed to fly out. Then later it developed symptoms of not charging battery and there is only power for the camera in general. I have image of the camera via wifi so the main board kinda works. The main board looks pristine, no corrosion, no visible faulty part. I have washed it in IPA just to make sure there is no hidden corrosion.
I have tested the caps and voltage regulators on it for shorts but nothing like that. If I plug in the charger led 3 and 4 blinks 3 times. I have hard time finding any info on what it could mean.
Since DJI parts are rather pricey I'm looking for recommendations how to figure out if the battery is the issue or the main board. I'm also interested if anyone has tips on what parts to check on the main board if there is any way for repair.
Thanks

[CapLeaker]

Last time I fixed a similar dead drone like that, I almost gave up. Same thing here, camera worked and the body didn’t. Got it as a botched repair someone trying to replacing a motor.
Fixed the botched repair, but the drone still didn’t work, only the camera. It also wouldn’t pair with the controller, but I could watch the camera on my phone. So I took it apart again and figured out the crystal was grounded out. No clock, no workie… resoldered a little spec that looked a bit off and 5 minutes later I flew the drone.
The drone was a different brand, but similar size to yours. The camera part is separate from the main drone part, so the main board kind of works is vaguely true. Look with the oscilloscope at the crystal clock and see if it is there or not.