Why won't my iPhone charge?

Katie Davies, " I left in some rice for about a week." can be part of the issue. Rice is great for cooking but it will not stop corrosion nor will it fix your phone. 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. I strongly recommend that you 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. While you clean your board, make sure that you inspect the SMD components, check for burned, charred, or missing components. Use a magnifying source and take your time with that. if nothing else check the "USB Fuses" and the charging coil see what you get on those. Check your traces very carefully to make sure that those are not damaged.

Once its clean, and you replaced the battery already, replace the dock connector and reassemble and re-evaluate for further (if any) damage. Hope this helps, good luck.