Maybe you should let them put the battery in it. Because like they said it is likely water damaged. Hopefully the bad battery wouldn’t have shorted out your charging port again.
If you have done all the steps like changing battery and resetting. It seems more like a motherboard level issue instead of a battery / charging cable issue
Your LCD display most likely blacked out. It would need to be replaced then should be good as new as long as no other components were damaged you should be good.