My iPhone has been charging an entire night but won't turn on?

It has water damage but was repaired with minor issues as expected. The last two nights its taken longer and longer for it to charge to turning on. Last night is the worst because its been charging for over 8 hours and hasn't turned on. AND YES the lightning bolt' symbol is on.

Anyone have this prob? I'm worried it will just never turn on again? Have you heard of this happening?

Added (1). Yes I've tried the soft power down holding both buttons doesn't do anything to turn it on

Did you try to soft reset?
Hold down power and home button together and release when apple logo appears on screen

If not, maybe it's your battery?