had a similar problem with a non-aquarised iphone 4. indeed it was the battery. after replacing it, the phone started again without the need to hook it up and without apple symbol bootloop. you could try that.

greets

Amjad, since it did have an immersion :-) the first thing I suggest doing is to not longer try to turn it on or charge it. It is easily possible that you are shortening out parts on the logic board i.e. the power management IC. If anything, disassemble your phone using these guides. Once you have that done, clean your phone with high grade isopropyl alcohol and this guide. It was written for a 3g but all the points are valid for your phone as well. Once its clean, replace the battery and re-evaluate for further (if any) damage. Hope this helps, good luck.