P8 Lite 2017 - is it time to throw it away?

[Acorn50]

Over the past 12 months my son has managed to crack both the front screen and back plate on his phone, and was complaining that it wasn't holding it's charge for long. Finally last month he dropped it into a swimming pool. He managed to retrieve it fairly quickly and dried it out - it started up okay with all the sounds etc. so we decided to change the broken screen and back plate. All went okay until we tried to charge it up after the repair job - no signs of charging, so bought a replacement battery, opened it all up again and fitted it. Still no signs of charging - the new battery stays at 60% and no green icon or movement. Also the screen dims to almost black within a few minutes. So, thinking it might be a problem with the connectivity of the USB port on the phone we bought a new internal USB port for it. It's still the same - battery doesn't seem to charge and the screen dims really quickly. The phone and apps all seem to work fine but I just don't know where to go from here. Is it time to admit defeat or is there anything else I can do. Thanks in advance.