@giroigosaerno start by replacing the battery with a new one. Keep in mind that water damage is the hardest to troubleshoot and to repair. USe something like [https://www.youtube.com/watch?v=ArNkAuf5GYI|this video] to do it.
While you work on your laptop, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.