I hate to be an additional downer... but I have been in RC Heli's for a long time - and aside from plastic - you cannot rely on anything really surviving a salt water bath. Even if a component miraculously seems to survive for the moment, you run a great risk of sudden failure in the future. I...
I have heard of several people having this issues on another forum (phantompilots). No-one seems to be able to pinpoint the problem, but from what I can see - I kind of suspect it is perhaps a bad batch of batteries. I would contact DJI with the exact info above as I have also seen people...