Chosen Solution
My iPhone XS get water in and stopped working. Apple said they can do nothing but replace the whole thing. Then I opened my phone with ifixit tools and dried the water. The device still not working. But I find that If I first plug in the charging cable without battery, then attach the battery to motherboard, it gives a repeatedly beep, roughly every two seconds. However If I attach the battery before I plug in the charging cable, nothing happens. What is this beep for? It is from somewhere around the taptic engine near the cable slot.
In this situation it would indicate a faulty battery. Replace the battery and it will most likely stop beeping. If it has seen liquid there might be other problems but you will need to replace the battery to start with.
