Chosen Solution

So I have a Apple iPhone 6S which had a battery problem the battery would go from 100% tot 20% in half an hour without doing anything. I changed the battery and now it just’ it shows the apple logo 2 times and theb boots to the lockscreen and then shuts down and shows a drained battery symbol. When I plug in the charger it shows a charging symbol, this happens only when it’s turned off but when it’s on the lockscreen just before it shuts down I can see that It doesn’t show the charging symbol in the top right corner. Is it a software issue? Or is it a problem with the new battery or the IC chip? (ps: the phone had waterdamage from rain which was fixed by someone else) Thanks.

While the phone is damage by water there is so many issue happened by showing that fault that clearly shows that there is shorting on the phone open it and check which area is shorted and change faulty parts.