I have a salty water damaged iPhone 4

Murathan Araz, " resting like this for a while. (maybe 6-8 months)" let's hope it is not resting in peace forever. the major issue you will run into is corrosion damage. Salt Water will get your components to corrode very severely. The very first thing I would do is to disassemble it by following this guide. Take a careful and close look at all components and connectors. Truly assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,.Take a look at all connectors as well as cable ends. After that I would suggest that you clean it a couple of times in sterile water, no drinking water. (that might have helped right after it got submerged in the sale water). Use a soft brush and clean it very, very thouroughly with the sterile water. With the amount of corrosion that I envision, you will most certainly have to remove all the EMI shields. Once you got the gross contamination cleaned, use 90%+ isopropyl alcohol and clean your parts some more. For a proper cleaning, use this guide. It was written for a 3G but it is still pertinent to your phone as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning. Do not use compressed air for the cleaning since that can drive liquid as well as corrosion particles into areas that will cause trouble later on. Do not use drinking water, if you need to use water, use sterile water. Also you do not need to leave it dry for a day. Isopropyl alcohol in the higher concentration will evaporate quickly and dissipate the water. The importance here is the cleaning. Yes, do replace the battery for sure. Use this guide for that. I would also prepare to replace the dock connector. With the month long corrosion, I suspect plenty of damage to the pins, that may be irreversible through cleaning. Even with all this, there is really only a small chance that your phone will work, but I definitely would give it a try. Hope this helps, good luck.